Sports was a big part of my life until I neared the teenage years and got a condition called osgood schlatted in my knees because of all the abuse I was giving my knees working them out so much. Think I was 11 or 12 when I went from practicing 3 different sports (freestyle athletics, gymnastics and football) while cycling and playing football in my time off to playing card games and reading books to pass the time.
I was able to hold my weight pretty well back then simply because children burn a lot of calories growing yet don't gain muscle mass as easily as advlts do. Yet ever since I got osgood schlatter I've gone from being pretty strong for my age to being pretty weak for my age but I'm still really slim and weigh little for my age. I'm about 65 KG right now and I'm 170 CM tall (or short if you like) and 19 years old. My friends are at least 80 KG or so, even those as short as I am.
Also cars are expensive

but I've ofc been kidding around really. I think the key for me to gain weight is not to try and gain it by eating but by working my body and gaining weight through muscle mass.
I'm sorry to hear that you had to quit sports due to that, but you seem to be really passionate about the stuff you've picked up after quitting and that's a great thing.

I still play lots of sport in my sparetime, but I'm struggling with injuries aswell. I will eventually try to get into a football team in the norwegian divisons but it's a risk for me health-wise.
My friends are more heavier (but also taller) than me aswell. I'm 170 CM and 60 KG so we're pretty similiar when it comes to that.

Also cars are really expensive, and I'm literally spending almost all my money on my drivers license which I'm undergoing at the moment. I imagine these shoes cost a small fortune too aswell.