Is being an adult really that bad?

I'm 17. I'm becoming an adult soon and It's one of the main reasons why I feel so depressed. It's stressing me out and I feel hopeless because I feel like my only real good years of life are slipping away.

A lot of people online complain about the rat race, having no free time, basically saying that adult life is horrible. I'm struggling to cope right now, if it gets a lot harder then I really don't see the point in living past 18.

Is being an adult really that miserable? How do you still make yourself happy?