We have to admit a truth here. The skin is elastic and after so many years of being stretch it is not very likely to return to it's former tightness, especially after losing that much weight. This is even more likely after you reach a certain age (50 something for you). That flap between the tricep and bicep is a result of this. See that all the time in former fat people , mostly around the midsection, neck, arms, inter thighs, etc,. People are fighting past gluttony and age.
Props to you for losing all the extra fat and getting back into BB'ing. By all means focus on these guns and get them to be the best that they can be. As for that extra skin flap, minor surgery could be the only option. Exercise, though offering many benefits, is limited in this regard. Good Luck.