Turning 20 with nothing to show for it

I'm 19M and turning 20 in November and I just feel a bit down about it. Everyone says that being 20-21 is meant to be the best part of your life but I don't really feel anything. I also heard that the holiday between A-level and University (the break between the end of school and university for Non-British people) is meant to be the best break of your life but I didn't do anything. Everyone I know is going out, having fun, doing cool stuff, in relationships. They all have something cool thats going on and I feel a bit left behind. I have one good friend, no relationships ever in any way, been trying to go out and do stuff but no one to really go with, a load of other stuff. It just feels very isolating, like I have and am wasting the supposed prime of my life. All I can say I have is playing instruments and writing, producing my own music which essentially means me sitting in my room working on stuff by myself... which also feels like losing the time I'm meant to be enjoying. Over the last 10 years of my life I have so few moments I can look back on fondly which are drowned by a bunch of sadness and isolation. I'm just feeling a bit lost and not sure what to do...