All old people sag - fact. No training will avoid that. Even skinny low fat triathlete oldies sag. You either get lucky or you don't.
Look at Stallone...as roided up as he is, he's in top nick for a man in his 60s...very defined...but you can see the age; you can see the sag. Nothing can be done. Deal wit it.
Keep the fat off and that's the best you can do.