Can I repeat TY at age 18 due to my unique circumstances

Retaining the facial features is something that can't really be done or prevented to be honest. I know guys who looked in their 30s at 15 & others who still look 15 in their 30s. It's genetics and how well you take care of yourself that influence that. Apart from having cosmetic surgery. There are hormone blockers but most of these are either design to delay puberty (so would need to be taken before it starts) or ones designed to help those who want to transition. Neither easy to get without a huge need case being put forward by medical professionals.

Exactly - some people age quicker than others! When I was in school there was a guy in 2nd year with a full blown beard & mustache. Dude was 14 but looked in his late 20's at least! Whereas I was getting ID'd in supermarkets buying a bottle of wine in my late 20's. It's not something you can really control. Well as a guy you can do a little in that generally men who are clean shaven look a little younger longer but that's about all really.

OP you need to stop dwelling on what you did or didn't do 2/3 years ago. God if I looked back at the time I wasted doing nothing as a teenager, I'd be in a bad way. It's what you do as a teen. And you only learn to try to make the most of things as you grow up. I would love to go back to easier days of not having as much responsibility or stress in my life but reality is that I can't & dwelling on it is not going to change what was or let me do anything now.

You really need to get some counselling about this idea that the end of teenage years or 18 is some massive step forward. Realisitically I didn't notice anything from the day before my 20th birthday (when I officially left being a teenager) to the day after. Nothing magical happened. I mean I feel out of sync with my actual age - if someone was to ask me, I'd have to think for a minute before replying because I'd probably auto reply about 5 years younger than I really am. But day to day, that doesn't actually affect how I live my life. Age is just a number that notes how long you've been alive. It doesn't denote anything to do with experience, wisdom, knowledge, feelings etc. You need to stop giving the number all this power over you.

Have you gone to your GP and talked about all this yet as was suggested previously?

Yes but my point is, I didn't do any mad afterschool activities at any point during secondary school & it hasn't affected me one bit in my adult life at all. Nor do I have any major regrets about it.

I'll be real with you. I was bullied horribly before starting secondary school. Thankfully went to a school where no one knew me so didn't know about all that so somewhat fresh start. Except I was so lacking in confidence that I made very few friends for the first 4 years of that time. It was only in 5th & 6th year that I came into myself. I didn't do one afterschool activity - no sports, drama, clubs or anything. No interest in them. I read & that was about it. I could wallow in what I missed out on & get caught up in it or I could realise that those things do not define me as a person at all. I didn't start finding the things I enjoyed doing until college. And some not until I was in my mid-20's. That is life. It's not something you need to know now but something that you are constantly learning & evolving.

As for Covid - I do completely empathise as we were all isolated during that time & a lot of it has lingered on just because of the way things have gone.

Genuinely though, & I mean this nicely, you need to stop dwelling on what you haven't done in the past couple of years & look at what you are doing now & what you want to do in the future. Reliving that time is not going to magically change things or make them better. It's not going to stop the effect bullying had on you. It's not going to alter the effect covid isolation had on you. The only thing that will change those is looking forward & trying to address those things in the future as opposed to some do-over button. Because even a do-over will not erase those years.