Most of those things are overrated if it's not something that you naturally enjoy.
Festivals- music is great but the lying in the mud/heat worrying if the next gas canister that gets exploded is going to land on your tent is a bit blah. I never feel like I can really relax because there's so many people off their nuts it makes me uneasy about my personal safety.
Girls holidays- never went on one so wouldn't know.
Drugs- yawn, glad younger people are starting to see them as boring. Ditto drinking. I used drinking as an emotional crutch and liquid confidence, which worked about as well as you'd expect. Usually lead to very regrettable one night stands.
Concerts- ok these are fun, but only if you're into music!
Travels- gap years weren't so much a thing when I was at that age, only one or two of my friends went. Watch the inbetweeners second movie- all that bullshit about finding yourself and not knowing a place until you've trekked barefoot drinking nothing but curdled yaks milk... Blah. Nothing stopping you going as an adult though!
If you feel like you're missing out, why not try doing some of this as an adult. Larmer Tree (hippy) or Rewind (80s) festivals are fun and pretty relaxed and easy going, or your local town might have "Townfest" day festival.
Pick a travel destination, research a couple of places you'd like to stay and grab some Airbnbs a short drive apart. We did this in Madeira earlier this year and it was AMAZING!
I still wouldn't bother with drink, drugs or one night stands. The older I get the more I think that these are things that take from you, rather than give to you.