I think this is the approach. My dad got a bike at 80 when he was no longer able to walk as far as he wanted, but his balance wasn't up to a two-wheeler. He got a trike and rode it until a few weeks before he died at 83.
Two points: we had a really hard time finding a decent quality trike, and finally settled for one that was pretty much junk. I reassembled it and kept it tuned for him, but it was made for riding three blocks to the grocery store, not even three miles around the lake. He'd been active all his life and would have done 10-15 miles into his 80s. And he was 6'2", while trikes seem to be designed for people about 5'6". Seat posts and stems can only do so much.