I started at 14 too. This was recorded on my 15th birthday [Invalid or Expired Link Removed] (August 22, 2010)
This is from February of this year.
I still suck, but I always suck less than I did 6 months ago.
Honestly, start with a good teacher. I quit my lessons after a year because I was tired of my teacher's attitude. But I got the foundation I needed.
Then continue studying your theory. Talkbass was the only teacher I had for theory and I know a whole lot more than the average musician at this point.
And finally, find, join, or start a band! Joining a band was the absolute biggest jump in my skills. At first it was once a week or every other week, but then more and more frequent. By my sophomore year we were practicing Monday, Wednesday, Friday, and Saturday whenever possible. Monday through Friday it was 4-8, Wednesday it was 3-8, Saturday it was roughly noon until whenever (usually between 7 and 9:30). That's a lot of practice time.
I played gigs with those guys, even out of town. I got to play to my peers. That video of us at our battle of the bands is one of my favorite memories. It doesn't matter that the performance was way worse than I wanted, that the singer had only been singing for a couple weeks, or that the screaming audience was excitable because they were 14-16 and most had never been to a real rock show. It was just awesome. I also met my girlfriend.
My freshman year, I was in the guitar club and I helped out with the battle of the bands. I said to my friends "I"m going to be in that next year."
The next year I had a band. We were new. We played first. We stood still, no stage presence, and the singer (who became my girlfriend after we let her go) was afraid to sing so she wasn't singing loudly enough to hear herself in the monitors. It was pretty bad. That year I said "Next year I'm going to win the battle of the bands".
My senior year (I skipped Junior to get out of dodge as soon as possible) I won the battle of the bands.
I graduated in June, the band has since broken up, and I'm on new projects now. Being in the band and putting my all into it is probably more satisfying than anything else I've done in my life so far. I miss giving my everything on stage and to the music. I'm just now finding a new band where that can happen.
Moral of the story, joining a band is great experience, and if you want something, just put your mind to it, learn from the greats, and do it. It doesn't matter if you suck. You suck a little less than yesterday. I know, relatively speaking, I don't suck. I'm actually a somewhat decent player, especially compared to where I was. We're all walking life together, not against each other, and that doubt is normal. Jimi Hendrix didn't think he was better than the pop singers at the time. In fact, there's a scientific study saying that the more you know about a subject, the less likely you are to actually feel confident -- those who don't know what they're doing are, typically, the ones who think they're great. And the reality is, you probably don't suck like you think do
Go out, join a band, and conquer your little slice of the world