20-Year Prospect
If you're thinking about becoming a rock star, like it's a choice or something, why on earth are you reading this? Seriously? Can you hear anything over the roar of the crowd and the pop of the champagne you're presumably bathing in? Since so much of this career is the luck of the draw, your genetic talent, and getting noticed by the industry, it's more on you.
Let's pretend for a second you care about job growth here. Well, it's slower than average (source). Are you seriously still reading this? Don't you have some incredible solo to write?
The job is actually changing these days, and not just because of all the drugs. The industry itself has been altered by the Internet. You know the Internet. It's what you're using right now.
Did you turn around to see if we were standing behind you? Good.
Nowadays, anyone can be a musician and put their music up for all to see. That doesn't mean they'll be paid for it though.
You want something terrifying? You're not immune to automation. You think you are but (presumably mad) scientists are perfecting robots that write and perform original songs (source). We're guessing most of their songs are about the eventual uprising...and what a jerk John Connor is.
Unfortunately, barring getting famous, this isn't going to be something you do for twenty years. Not full time anyway.