Your parental figure can be younger than yourself.
I had a thought running through my head lately.
Y'know when a character in a piece of media is often interpreted as a "mom" or "dad" or generally as a parental figure for another character or a group of characters ? And that parental figure is usually not much older or even younger than their "child" ? We usually see this in casts within the same age group ( exemple : highschool settings ).
In these situations, a lot of people's reaction is to say things such as " oh they're too young to be a parental figure ! ", " their so called child is too old to be realistically theirs ! " and the likes.
Well then, let me tell you a story.
When I was a child around 8 or 10 years old, I would often go over to my cousin's house, not far from mine, for her to not be alone when her dad was at work and her mom at her psychiatrist's office.
You see, her mom has depression and other mental illnesses mainly because of miscarriages she had trying to get a baby boy, even after 4 girls. My cousin was the 2nd girl. That's why even if her mother loved her, there always was disappointment in her gaze. My cousin was always so miserable regarding this.
So, I spent all of my time with her. I would wash and brush her hair for her, and tie it up for her, even if she could probably do it better herself. I would make tartines as afternoon snacks with a few peices of bread and any fun condiments i could find in the fridge. I would ask what she did this week end, if she wanted to try a new game even if I wasn't interested in it, rowdy play like dads do; heck, I would dry her tears when she cried, cheer her up with the sweet words of a mother. I would patch up her skinned hands and knees when she fell, and kiss it better.
She is a few months older than me.
And yet, this child told me, a younger child, that I felt more like a mother than her own, the women that is my aunt.
My point is, in this case, age IS just a number.
If you feel like a true parent to one of your friends, or if one of your friends feel like a parent, and if the opposing side agrees, then CONGRATULATIONS !!!!!! You now have a found family !!!
And for characters, you just GAVE THEM a FOUND FAMILY !!!!
AND REMEMBER ! Technically, an 18 year old can adopt a 17 year old !