You know what man, be yourself. You won't be happy being in a relationship with someone if you have to pretend to be someone else. Some girls might find it charming that you get such enjoyment out of such dumb jokes, I know for a fact that there are girls with a similar sense of humor.
I'm 22, and I am also ridiculously "immature" when it comes my sense of humor. I laugh at some of the dumbest shit xD and it's great tbh (well I enjoy all forms of humor, not just the infantile). Better to laugh at a lot of things than to be boring and "mature". What's great about being mature if all it means is that you enjoy less things than kids? Real maturity is not conforming to what society says is acceptable for adults and just simply enjoying what you enjoy.