A lot of us started bicycling over 50 - I started at 58 (am now 69)

Within 3.5 months I rode 358 miles over Colorado passes in a one-week tour. My wife, now 71, is fully capable of riding 25-40 miles. She started about 62 years old.

My point being, don't sell your parents (or yourself) short. I and my wife started on mtn bikes (which we still have and ride) with slicks instead of knobby tires.

I think a mtn bike or a hybrid would be ideal as a starter bike.

A big soft seat may be ok for a short ride, but on a long ride it will expose a lot more skin to pressure. Ideally, a seat should support your "sit bones" - which is the reason for those narrow seats - but that may be something to worry about later