that's a big jump in mileage and time in the saddle. you will feel it. it's not that you're a slouch mileage wise, just not having been on the bike for extended period of time.
that being said. do it anyways. take a lot of breaks, eat and drink. stretch. smile your way thru it. it's a lot of fun.
my buddy did his first century a few weeks ago with little training (less miles than you) and you're probably more fit. around mile 80 he was complaining, but he made it to the end.