My first group ride I was invited along with a group of guys who belong to a group that ride extended tours, of about 50-60 miles a day for a week. They are all older. One of the group, who came with a recumbent, has ridden across America several times.
I was the only guy with a road bike. For the most part, they were more active and more fit, and had no problem keeping a good pace. I kept up, lead occasionally. On the downhill, I let it out, tucked and flew down the hill, on the return, they spun and I hurt.
Its entirely possible to do a century on a hybrid. I would suggest not just a thinner tire, but slicker tread for less resistence, and something that can take a higher pressure.