It's not clear! It's safe to say that Tom is at least 3 years older than Jake. In Megamorphs 4 (set at the same time as #1), Tom's a licensed driver, which puts Tom at 16 or older, and Jake is 13 at the time he becomes an Animorph (#53). So the age gap is at least 3 years.

However, #1 also mentions Tom quitting his high school basketball team, so that puts him at 18-19 at the oldest as of the start of the war. Given there's no mention of Tom being expected to start college or a full-time job at any point in the next 3 years, despite having upper-middle-class parents with college degrees, I tend to believe he's closer to 16 when the war starts and 19 when he dies, vs. 19 when it starts and 22 when he dies.

The Invasion is such an excellent one-two-three punch of an opening that I've never seen it topped in series fiction. Animorphs tells you EXACTLY what you're getting into with the first book.

We get about 3 pages of our heroes having wonder and joy at aliens being real before #1 hits us with the graphic onscreen death-by-cannibalism of this kind, caring stranger. And if Jake being chased by 7-foot blade monsters wasn't scary enough, he only escapes because a human bystander dies in his place.

So Jake goes home. To his nuclear suburban family, and his piddly sports problems, and his nice morph-training sequence with his friends. And just kidding there's a yeerk living inside your home already and it knows where you sleep. But that's fine, we'll just tell an adul — oh shit the cops are controllers the reporters are controllers the camp counselors are controllers the vice principal's a controller Elfangor really fucking undersold this problem.

So it's up to them, they guess. And Marco might be scared of dying, and Cassie might be reluctant to fight, but Tobias seems 100% confident they can save the world! So they go. And they don't save Tom, and they get people killed, and they do nothing to hurt Visser Three. And they don't even all make it home at the end of the day. Because it turns out Animorphs is not only a series where supporting characters die; it's a series where the main characters get permanently injured and will never be the same again.

JAKE: WEB → i think jake seems to exhibit a deep fear of being controlled, and i would argue it takes root in his psyche the moment he finds out tom is a controller. it only becomes more realized in #6 when he becomes a controller, and even MORE SO later on when crayak begins to torment him. it feels as if he despises the galactic chess game idea in general (whether it be crayak or ellimist), so it’s rather fitting that he was likely a wild card like rachel.

MARCO: BURIED → marco is seriously my favorite character of all time and thus this is impossible for me. he’s very hard to pin down, and i think there’s definitely elements of lonely and vast to his character, but i’m settling on buried. manifestations of it appear constantly throughout his life; his mother drowning, the emptiness of her coffin, him and his dad being extremely financially unstable in the wake of her death. you could argue there’s a buried aspect to the weight of having to destroy eva, whether that be from team pressure, his own logic, or her own assurance that he will destroy edriss.

RACHEL: SLAUGHTER → i figure this is likely easy to understand, but nevertheless: rachel is scared of becoming a killer. she is scared of being hungry for bloodlust, and furthermore, she is scared of other people seeing her that way. see jake monologue in #22.

CASSIE: DESOLATION → i think cassie is typically opposed to destruction, but i think she is actually scared of being the destroyer. the book i think of specifically is megamorphs #2, in which she loses herself in t-rex morph (a morph she was against doing in the first place) and has an understandable breakdown over after returning to her senses and discovering she killed another dinosaur. though it’s in a similar vein to rachel’s slaughter fear, i think cassie is so dedicated to conservation that the opposite being inflicted by her own hands is a nightmare for her.

TOBIAS: FLESH → when it comes to tobias, i think there are two options at hand. one is, obviously, the hunt. early books have him fighting the hawk’s predator instincts, feeling disgusted by himself and attempting to “stay human.” later on, he gives in to those instincts, though, so i think a more interesting fear assignment is flesh. flesh focuses on the dysphoria tobias wrestles with, typically pertaining to his human form. the book that best exemplifies this is #33; he is deeply uncomfortable in his human form, and is simultaneously afraid and paranoid that rachel is intentionally trying to trap him in it.

AX: CORRUPTION → if there’s one thing i know about ax, it’s that he’s deeply repulsed by yeerks (for better or for worse.) he does not see them as people; they’re akin to disease to him. specifically recalling the scene in #29 in which cassie has aftran infest ax— GRANTED, this is done without ax’s permission and he has every right to be deeply upset at that violation, but he seems even more angry at the fact that a yeerk was in his head at all.

also, in terms of the series as a whole, i think the main fears the kids would be fighting against would be the extinction (whether real or not, this would be similar to jon trying to stop it in s4) and the stranger.

Huh. I feel like the closest we get in canon is Erek. Where despite being their ally, he's clearly got his own agenda. And on several occasions (most notably when he prevents Jake from saving Rachel in #53) he works against the Animorphs.

Even in #10, Marco and Jake are pretty open about not trusting Erek's character as much as they trust his desire to end the yeerk threat. That remains pretty consistent throughout the series: Erek saves all the Animorphs and lies to them about the nature of the howlers in #26, and he states outright he won't help them in #43 and #47. So like, Erek isn't a full classic trickster, in that he's entirely lacking charisma and has clear ethical lines, but he is that guy you ask for help only when you don't have anyone else to ask. And he's a lot more wily than the Animorphs themselves — keeping yeerks captive to maintain his ruse, pretending to be other people or making himself invisible at will.

Ax: Rattlesnake! It's small, it's fast, and it's capable of taking down even an andalite (let alone a human) within seconds — usually without killing. IMHO this is the perfect blend of stealth and offensive power for an Animorph, especially because it can take a controller down without killing the host. Plus, it has plausible deniability if anyone does see it around, as a species native to California.

Marco: Cobra. Ibid everything I just said about rattlesnake, but with the added bonus that it's even faster. Plus, I'll never not love the moments in #21 and #37 where someone yeets cobra!Marco at their problems.

Jake: Anacon Okay, fine, I'll get off the snake train. Howler, then. It's got limited utility since it's basically a bomb: it can kill everyone in an area, or it can kill no one. However. That one anon specifically suggested using howler on the Blade ship in #54, which is a perfect use case, because the Animorph in question would be alone and surrounded by dozens of controllers.

Cassie: Rachel. I love Animorphs' concern with consent as being The thing that separates the heroes from the villains, and I understand how that translates to almost never using human morphs because you need the DNA donor's permission. But I love the idea of Cassie being cornered, about to be caught... and then morphing halfway into Rachel, because that's a thing Cassie and only Cassie can do. So now she still looks like a human girl, but one who's middle height with Black and white ancestry and mid-gold mid-length mid-straightness hair. And no one can identify her.

Rachel: Chimpanzee. Because they're fairly strong fighters, but can also use weapons. And Rachel is the most inclined to use weapons of anyone on the team, from the severed limbs of her enemies (or herself) to the dracon beams in #17 or #37.

😇