Impellers

I recently purchsed a 1993 Four Winns 18 footer. Has a 90 horse Johnson,Model #VJ90TLETS,which I fiure is a 93,What do VJ and TL stand for? One thing I am in question about,is the guy I bought it from,said the impeller is maybe 1 or 2 years old. Just how long do impellers last? I would guess they are made of plastic or some fiber material. If one is starting to go bad,how do you know and what do you look for? I ordered a used repair manual (Seloc) over E-Bay so i can figure how to winterize it at the end of this season and hpoefully get some more maintenance info,but was kind of curious about the impellers.