Being 60 is only middle aged these days. 
My dad is 62, and I don't think he is old. He swims daily back and forth 50 times in a university swimming pool.
Goldfish in fact require a lot of water, because they eat a lot and they are extremely messy - produce a lot of ammonia.
For a single fancy goldfish, you need minimal 20~30 gallon of water.
For common goldfish, you need 40~55 gallon for just one.
Betta on the other hand, it will be fine in a 5 gallon, heated, filtered tank. That is why I suggested a betta instead of a messy goldfish.
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