I think it's time for some moderate distance rides with hills and concentration on pace. Also be sure to add a couple of days each week for honest to gosh rest. Definitely taper off the last week before the century, focus on a good diet with lots of fresh fruit, complex carbohydrates and lean protien. And hydrate hydrate hydrate the last few days before the big ride. For me, a 75 mile ride the weekend before the century would not be a good idea, but I am 55 and have only been riding just shy of two years now.
It's all downhill from here. Except the parts that are uphill.