cool story, bro

First, we know a couple of things about his age from canon:

We know from "Chimney Begins" that Tommy was not a probie in 2005 when Chim joined. So he'd been there at least a year before that. For the sake of making him as young as possible, we will say that he has ONLY been there a year. We also knew that he "learned to fly" in the army.

So, that means:

He had to have joined the LAFD ~2004.

Had to have completed the necessary requirements for army pilots prior to that. For Army pilots joining prior to October 1, 2020, there was a 6 year service requirement after completing flight school.

To be a pilot, Tommy also had to be either a Commissioned Officer OR a Warrant Officer. Assuming he was not an officer, that means he had to complete all of the following before he could becoming a pilot: Army Basic Training, Warrant Officer Candidate School (WOCS), and Army helicopter flight school.

To make Tommy AS YOUNG AS HUMANLY POSSIBLE IN THIS TIMELINE: We'll also assume he joined the army at 17 with parental permission, which you can do because the USA is stupid and because his father seems like the sort - and also because we are going to make Tommy as YOUNG as he can possibly be in 2026 to prove my point:

Age 17: Graduates High school, Enlists in Army and does Basic Combat Training ~ 2.5 months

Age 17: Warrant Officer Candidate School ~1.5 months

Ages: 17–18 Army helicopter flight school (IERW) ~12 months (Can be up to 18 months, but we are making this the shortest timeline possible)

Ages 18–24: Aviation service obligation 6 years

Age 24: Leaves Army (Here, we give Tommy a LOT of assumptive grace. Getting into the LAFD Academy is hard, but we'll assume his officers wrote nice things or whatever and he got in right away.)

Age 24 :LAFD Academy: 22 weeks

AGe 24: Starts Probie Year

Age 25: "Chimney Begins" - has been with LAFD for at least a year. (in 2005)

SO, if he's 25 in 2005, that would make him born in 1980. In 2026, that that makes him no younger than 46. If he's born in 1980, that means he is 11 years older than Buck's 1991 birth year, which is fun and sexy if you aren't boring (and they are not.)

Notes:

Now, in truth, in a realistic timeline, Tommy would be older still.

He'd spent closer to 18 months in flight school and he probably had to take some time to apply/wait/join the LAFD academy, and maybe his parents weren't dicks and made him wait to 18 before he signed his life away to the military and/or maybe he gradated at the age of 18.

There's also issues with waiting for admission to WOCs and flight school.

And we have no IDEA how long he was in the LAFD before Chim came along

Honestly, 48 is more realistic and he could easily be celebrating his 50th birthday OR BEYOND. IF YOU AREN'T A COWARD.

BUT~ if you want him as young as possible, 46 is the bottom floor of what can be going on here in 2026. He can definitely be older, but he can't be younger and have the timeline make any sense.

In conclusion:

Sources:

(Just sources; don't join the military, kids.)

Army Aviation Special and Incentive Pay Policies to Promote Performance, Manage Talent, and Sustain Retention

LAFD requirements recruitment video

Rotary Wing Aviator Warrant Officer 153A

“He, uh, doesn't have anywhere else to go,” Evan said, the picking turned into full on shredding. They were going to have to sweep up the mess before going so they wouldn't get banned; it was the only coffee shop that employed a barista who hated everyone but him particularly, which meant she made the best coffee in the entire city. “Kameron’s family kicked her out and Connor was an only child. His parents and aunt aren't able to take care of Theo.” And then, a little guilty: “He needs a lot of attention.”

The old hurt snapped into anger. “He just lost his parents. Of course he needs attention. Jesus Christ, Evan.”

Evan jerked back a little, blinking rapidly in the face of Tommy's misplaced anger. “Hey, I know that, I do.” Evan said it gently, as if in apology even though Tommy was being an asshole. “I just meant that Connor’s parents were older when they had him, and now they’re not able to care for Theo. That's all.”

“No, I’m sorry. That was my own bullshit. I didn't mean to put that on you.” He scrubbed a hand over his face so he didn't have to look at the complicated face Evan was making. “So what do you need me for? Pretty sure your sister or Diaz can give you better parenting advice than whatever I could come up with.”

“You'd be surprised,” Evan said dryly, and pushed his unlocked phone across the table.

The kid that stared up at him was cute, and now that he was looking for it, undeniably Evan's biological kid: same nose, same beaming smile, same—wait. He zoomed in on Theo's smile, trying not to feel exactly like what his father always claimed he was. “Is that...?”

“He gets it from his mom. That’s why her family kicked her out.” Evan’s brave little smile wobbled. “Theo is, uh, he’s like—”

“Like me.” He couldn’t look away from that pointy smile. “Yeah, I don’t think Diaz is gonna cut it for this one.”

The cardboard sleeve had been reduced to its base components. Tommy passed his sleeve before Evan could start in on his cuticles.

“I know we haven’t—that I haven’t—” Evan broke off, frustration pulling the corners of his mouth tight.

“Just say it,” Tommy said, gentle even as he felt the telltale warmth along his spine. Thank god he’d been smart enough to go with a high collar shirt and a hoodie; the only skin showing was his face and hands, which were normal. Safe.

“There aren’t many people like him. Even the social worker doesn’t have many resources.” Evan set the cardboard sleeve aside. “It’s already so hard to be a kid, but this is going to make it—”

“Even worse for him?” He kept his tone level, but Evan flinched as if he shouted.

Evan shook his head. “Kameron and Connor should be the ones helping him and loving him, but now he’s just got me, and I don’t know what I’m doing.” Evan’s jaw set with that earnest determination. Nothing in the world was as devastating as Evan’s sincerity. “He needs people in his corner, and you’re one of the best people I know.”

Tommy closed both sets of eyelids. There it was, just like how he knew it was coming. Evan wanted what he could do but never just wanted him. He couldn’t even be angry about it; it was his own fault for never bother to fucking learn.

“Tommy?” Evan touched the back if his hand.

His opened his eyes. Right now, hidden under the shirt and hoodie and his sturdy boots, he was all lit up, a warning to predators that, hurt or not, the smart move was not to fuck with him. He slid his hand away.

“Does he have any other traits outside of the teeth?” he asked.

Evan stared forlornly after his hand before giving himself a hard shake. “I thought maybe he had like super smell, but turned out it was only for cookies. So just the teeth right now.”

“He’ll probably develop a couple more as he gets older. Puberty is a real bitch. I had terrible growing pains and I was itchy all the time.” The worse part was the never ending deep burns as he grew new nerves and cells and—well, changing in the locker room got a lot more complicated after that.

Evan perked up a little. “Oh, is that when you got the—”

“Yup.” That came out too short and Eva deflated a little. It was hard to tell from just a picture, but he’d bet there were too many teeth for Theo’s small mouth. “You should get him something to chew on.”

“Like a dog toy?” Evan said in an extremely scathing tone.

“First of all, the kid is what, four? He’s going to want to bite anyway but he is definitely going to want to put those chompers to work. And I’m sure they’re bothering him. Chewing will help.” Theo was too young to be able to tell exactly what kind shit got mixed in with the usual genetic make up, but Tommy had a feeling. “Has he lost any teeth yet?”

Evan squinted suspiciously at him. “You mean his baby teeth? He’s like several years away before his adult teeth come in.”

“I don’t think you have to worry about baby teeth. There’s a good chance he’ll lose and regrow them throughout his life. You’re going to need a good dentist. I’ll ask around.”

“Regrow his teeth?” Evan said, ignoring the bit about the dentist, which was fine. Tommy had that part covered. “Like a shark?”

He smiled. “How does the kid handle bath time?”

Evan made the face of every aggrieved parent. “He loves it when he’s actually in the bath, but he hates getting in or out of it. Transitions are hard for him.”

“They’re hard for everyone.” One last look at the picture before he pushed the phone back across the table. “We’ll have to take him down to the beach and see how he does with the actual ocean.”

“You think he’s really like—but you don’t have the teeth,” Evan said. And then, “Wait, we?”

Tommy gave his best nonchalant shrug. “I know what it’s like growing up with an extra rung in your DNA. Like you said, the kid is gonna need people in his corner.”

Evan swallowed hard, clearly fighting his own Buckley DNA to keep from crying. “Thank you,” he said softly, and this time Tommy let Evan take his hand.