Its little strange and scary that

You're plenty 13 in a way.. But our individual perspectives make us fear things like that.. our personalities originally come to be when we hit that age... Basically you just still feel like yourself is all.. people think that they're going to be different naturally but the only thing that will change us is hardships... We don't get a second puberty to go through after 13.. so it's to be expected, that unless some kind of trauma forms in your life.. You'll still feel like yourself.. Don't put pressure on you to change in any unnatural ways..

Same thing happens to me.
I'm MUCH younger than my chronological age.

oh the dreaded switch to an older age group year. I wish i could say it gets easier but it doesn't

Well, don't fret. It seems that you have a healthy self-awareness.

Yep.