on the plus side, you're self aware in a way that you've identified the problem and on the plus side, that's a lot of power to you already.
I strongly recommend seeking long term counselling. I can relate to a lot of what you're saying and what you're going through isn't unusual.
Ignore the age thing, life's not a race. I'm 21 and I still get over excited from doing things that most people have been comfortable doing for years but they're still quite new to me (i used to have social anxiety and was scared of all kinds of things and had all sorts of panic attacks and did a bit of self harm but now I'm gooooood)
I told you the above because if i can get out of a hole, and it was a pretty big one, you can too.
Know that you're not alone i what you're going through and although it may nto currently feel like it, what you're going through certainly doesn't have to be a forever thing. far from it.
you're still young and you've got a lot of fun to be had infront of you. Get the counselling, really emrbrace it and the the worlds your lobster (counselling helped me massively.
This may sound patronising in a way that doesn't work for you but i mean it in the best possible way when i tell you that people will envy you for enjoying the small things in life once you feel better: after not being able to get on a bus (for eg) with ease, once you're able to it's the best feeling in the world. You've got a lot of excitement ahead of you
Hope this helps