Neither the movie and and novelization give us much detail on the bowcaster Chewie is using. We don't know where it's from, how old it is, how customized it is, etc.
It's interesting to note that Han takes the bowcaster in the movie at least twice and shoots it, but no such scenes occur in the novelizations, implying they were last-minute changes to the script. (One explanation I have seen is that the director needed to explain how a single shot from the bowcaster was able to
seriously wound Kylo Ren enough for Rey to beat him
so he added some scenes of Han admiring the weapon's power.)
This means the only thing we have to go on is the one scene in the movie where Han asks to borrow the bowcaster, and decides he likes it and wants to get one for himself. The way the exchange takes place really only makes sense if there's something new and better about the bowcaster than the one Chewie had been using previously. Han doesn't even seem sure about how to use it for his first shot, and is surprised by it's power.
Even if he'd never used it in combat before, I find it extremely difficult to imagine that Chewie had been carrying around a strange bow/blaster hybrid weapon for 30+ years and Han never once even picked it up out of curiosity.
I'll also note that the weapon looks more powerful than the one from the original trilogy -- the amount of damage it does seems higher than previously. Combined with Han's seeming lack of awareness of how powerful it is, I think the only reasonable conclusion is that it's either a new, or newly modified, bowcaster that Chewie's carrying around.