Welcome to the 50+ zoo and BF in general. You have already heard the qualifiers such as the ritual colonoscopy, the required Pie affliction we all share and love, so just make sure you post pictures when you find a bicycle you like.

As other said a used bicycle from a good Local Bicycle store (LBS here) or on Craig's List could allow you to get a better quality bicycle that will make riding more enjoyable. Even if that shop you visited doesn't have any used bikes they or another LBS could be enlisted to look out for a suitable bike for your needs. Maybe a rider looking to upgrade and has a bike they would sell you in order to facilitate their N+1

Most important thing is to get a bicycle that fits you properly. An LBS can fit you and set up the bike to suit your size and riding usage. Even if you buy elsewhere they may well "sell" you a fitting in order to get your future business. Once you are riding regularly and get in bicycling fit shape you will at a minimum want some changes such as spares, upgrades to bars, wheels, etc. What type of riding do you want to do? Road/MUP, off-road, touring, commuting, give us some input and the experienced hands here can be a tremendous help to your decision making.

Congrats on that super weight loss you hae accomplished, that shows some real initiative and commitment to your health. Do stick around and let us know what you decide or need help in doing.

Bill