Can you loose the weight after you gain muscles?

It is absolutely essential that excess weight be lost before muscle-building begins. Otherwise, your muscle will not truly be muscle. It will only be fat that has taken on a muscular appearance. Once you discontinue the program (for instance, at an older age) instead of retaining the muscle structure, it breaks down back to a fatty state.

This is essentially flab - muscle that has returned to a fatty state. When you have lost the excess weight, then develop true muscle. True muscle, unlike fat, does not give out after a few months of discontinuing a building program.