how can i bridge my mental age gap?

hello all. i hope this is the correct subreddit as google search for a similar question brought me here.

i am currently on a gap year after realizing that i was mentally unfit for university. and yesterday whilst trying to rest in bed i recalled the cringe moments i had back in high school. and they made me realize something. back in 11. grade, i was 11. grade only physically and people perceived me like that when my mental state, thoughts, mind was all stuck at 7. grade. because of this i also did not know some things 11.th graders were supposed to know, such as; how to establish a healthy communication, the social consequences of my actions. this in return made me realize everything.

which are, off the top of my head; why i felt inferior to my peers, why i had to drop out of university, why my "successes" did not feel like successes, why nobody wants to talk with me, why i can't get any sort of long-lasting friendship and why i feel sadness and anger when someone mentions my physical age.

it is because i am currently a 15 year old in the body of a 19 year old. (yes, i feel like i managed to mentally age 2 years since eleventh grade. i don't know how, probably due to my brief university pursue.)

and i feel like resolving this will fix a lot if not all of what's wrong with me and my life. i thought that if i, by myself, at least mentally age 2 years and close the latter gap with a special program i am thinking of participating later this year, that would be fantastic. i have identified a few points that can potentially be used to resolve this age gap however i don't know how to take action on them. i will list both below for convenience:

1. process the fifth grade trauma (i don't know where to start with this though. maths? the discomfort i feel towards big [especially big and empty] spaces? bodyshaming which i thought i ended at 10th grade?)
2. getting my neurodivergence formally diagnosed (not possible yet)

since second is not going to happen until far future it can be ignored. where can i start with the first point?