Nobody's mentioned multihulls. Most octogenarians won't feel comfortable on
a boat which is likely to heel at least 20 degrees in any middling wind.
Multihulls are likely to be a lot flatter. Some trimarans have decent
cockpits.

The other problem which has been noted is sail handling and, between the
Nonsuch wishbone catboats and the Hoyt boats (Alerion xx) with self-tending
jibs, that's a help.

I'm building a 28' daysailing tri, Dick Newick's 'Spark', which has a
Ljungstrom cat-yawl rig. There's a lot that's experimental in the rig, but
it's hoped that it'll be easy for an old fart to operate. Ask me in a year.