At one point or another, if you are serious about playing the guitar, you need to go out of your house with your guitar. Just grabbing it by the neck and throw yourselves at the bike could damage your instrument seriously, especially if you like to do a bit BMX or FMX when you go around town, or if you like to drive out in the road in front of large trucks.
So, what should you do then? You probably got a cheap bag with the guitar when you bought it, a bag that in most cases is nothing but a piece of woven nylon made into a guitar shaped bag. If you are lucky, it was a bit padded.
So head down to your local guitar store and check prices for padded gigbags or even better, cases. Guitar cases have a hard shell that protect your instrument from damage, and I think cases are the best way of protecting your instrument. However, as a young 14 year old guitarist who is gonna ride your bike to band practise, a gigbag would be better, as most bags have straps so you can carry it as a backpack. I will recommend you to check out Ritter Bags, 500 series or better, as they are really good. They are well-padded, they are waterproof (or resistent, at least), and they have lots of pockets for you to put all your gadgets in (notes, cables, tuners, fx boards and pedals, extra strings, you-name-it), Also, they are one of few independent bag companies I’ve seen that make bags for odd-shaped guitars, like BC Rich or Gibson Explorers.