When is it safe to start with a gym mucle-building regimen? Afraid my muscles are developed unevenly now and am inflexible. I get cramps in my legs when having sex. I'm bad at stretching. I can't bend over and get anywhere near my toes. Also have mild sco

Stretching . Stretching is far more important in your case that building muscle mass. Don't fool yourself. I would look further into that leg cramping with sex. At minimum your calcium and potassium should be check and further evaluation should me made into a possible radiculopathy. Get the kama sutra and look for other positions. This can be a lot of fun. You can see a physiatrist or an orthopedist.