As someone who just started playing 5 months ago myself, the only advice I can give is patience and practice SLOWLY!
I been going through a bass beginner book myself, and there is many times where I get frustrated trying to play along because I'm just not ready to tackle that particular song or chord progression. I need to slow down, and practice it slowly, it sucks because I can hear it in my head, how it should sound, but the fingers just fumble and mumble, however, in time, and usually faster then you anticipate, it will click.
Also music theory.. yeah, good luck. Just try your best to "fake it" until it clicks. Alot of what your learn in those books won't make sense at first, but you just have to trust yourself that eventually it will make sense. It's just like learning a language, with time and patience, stuff will start falling together. I've experienced this recently with certain scales and songs that I been trying to learn, just a week ago I just had one of those epiphany moments where I was like "OH! its like THAT, okay, now I see how that works" and when you hit those moments it just motivates you to keep going.
As others have mentioned, you starting at a good age, I started late (Just turned 28) so I missed out on alot of those years when your mind is fresh and stress is less. Take advantage of this time son, you will be light years ahead of us by the time you get to our age!