GO FOR IT!!!
You can practice in your bedroom all you want, but being in a band will teach you all kinds of things that can only be learned by experiencing it first hand. As you stated you are young and have plenty of time, but the sooner you get moving on this the better you will get at it.
There are a couple of things to keep in mind in terms of attitude going into it.
1) BE FLEXIBLE
Take the time to listen to your band mates before jumping to a conclusion. You may learn something, or you may teach them something. Basically try to understand their point of view, and go from there, whether its a specific chord change, or something larger in terms of "artistic direction". Make sure everyone gets a chance to express themselves and you'll be in a happier situation. You may not like a particular song but maybe one of the guys really digs it. Decide as a BAND what to play and what not to play. If anyone's not happy... drama starts.
2) BE PROFESSIONAL
Don't waste other peoples time by showing up late or pulling a no show. If you need to cancel for whatever reason, let them know about it BEFORE the guys start packing up their gear. Don't make them lose a Saturday because "I forgot".
Be prepared to play. Practice is what you do on YOUR time, rehearsal is what you do on band time. Do NOT wait until the bands all together to finally get around to starting the stuff you were supposed to learn last week. Yeah I know.... more homework. And remember nothing says that two of you can't get together to hash things out prior to rehearsal.
Pull your own weight. Load up equipment like everyone else. Help the drummer set up his kit if you need to, or have the drummer help lug out your bass rig since you helped set up his kit first. Yes even the singer has to get dirty with the gear unload/haul away. This also relates to finances. Don't be the "financial sponge" or the "bank". Keep a close eye on your budget and don't borrow too much, or give out too much. Let guitar guy pick up the tab for his own strings and the drummer his sticks. It is okay to help them out in a tight spot, but don't make it a habit. Just sayin'
In short be responsible. Getting an early start like this will ensure that other musicians will love having you around. As soon as you become unreliable or untrustworthy your done whether in a band or just in life.
3) SET REALISTIC GOALS.
Everybody want's to "Make it!" but few actually do. Pick something achievable like getting 3 songs ready for a school talent show, or having the band put together a list of tunes to cover, learning one a week until you really start to gel as a band. Once you have a minimum of a 30 minute set play at a friends birthday party or back yard BBQ or something.
4) TAKE CARE OF YOUR EQUIPMENT.
It doesn't matter how much it cost or the current condition its in. Don't break your stuff, or anyone else's. If you do bust something, even on accident, bring it up immediately, before they find out about it without you telling them first. Talk with the owner on how you will smooth things over. Even if they say it's ok and don't worry about it, find something you can do like buy lunch or some small gesture of grace.
Continuing with the gear theme, don't worry about whether or not you have the latest and greatest or what is thought to be the best brand. Do NOT buy any brand simply for the name thats on it. Buy it because you love it. I have custom made basses made with incredible woods and amazing electronics, but I also love my $200 completely stock Squier P-bass special. Rock what you got and don't get too caught up in the "shiny" stuff. Is there a difference in gear quality? Of course there is, but don't be too worried that you don't own it yet. You will get some of that soon enough.
5) NEVER EVER STEAL SOMEBODY'S GIRL/GUY!! EVER!
This is a biggy. Your band mates "significant other" is OFF LIMITS especially if they're hot. Hugs and/or a peck on the cheek are one thing, but any more than that is just a powder keg of drama waiting to happen. Don't do it!!
So to wrap it up (there are more points I could make but I'll spare you from that for now) have fun! Be courteous and respectful of your bands time, equipment, and relationships. Allow people the room to be themselves and in return they will allow you your own space to be creative and discover who you are and the musician you want to become.
JOIN A BAND AND GROOVE ON!