Start hunting for a group of over 60 peers that you could organize small group rides with.
Talk to the group organizers and see if they have a list of members, their ages, and contacts, and get a list of riders over 60 or so. Potentially even going into past membership records.
Talk to local bike shops. Perhaps make up a flyer that they could give out to anybody they think might fit the bill.
Friends and family contacts. Perhaps even go to exercise gyms and look for elderly individuals using exercise bikes.
A geriatric physician might even be able to help you find some contacts.
Join Strava. I think with a paid account you can sort riders by age or speed. I've found talking to other cyclists is frustrating, but you can add them as friends, or make comments on their rides.
Join, or create a local "Classic and Vintage" cycling group. It is extraordinary how many grey haired people show up on ancient bikes.
On the opposite end, make sure you keep your own bike up to date. So, don't push around a 50 pound Schwinn trying to keep up with people on carbon fiber bikes.
If you do go on solo rides, are there any nearby off-street bike paths that would meet your ride objectives, even if you have to drive to the start? Rails to Trails?