Yes, it's correct. It's also the title of a Bob Dylan song: "Forever Young" May God bless and keep you always May your wishes all come true May you always do for others And let others do for you May you build a ladder to the stars And climb on every rung May you stay forever young Forever young, forever young May you stay forever young. May you grow up to be righteous May you grow up to be true May you always know the truth And see the lights surrounding you May you always be courageous Stand upright and be strong May you stay forever young Forever young, forever young May you stay forever young. May your hands always be busy May your feet always be swift May you have a strong foundation When the winds of changes shift May your heart always be joyful And may your song always be sung May you stay forever young Forever young, forever young May you stay forever young.

Yes, "forever" is an adverb that can be used before or after the modified verb or adjective. When used before, is has a bit more formal or classic sound, at least to my ear. When used after the modified word, the meaning tends toward "without ever ending." When used before, it also caries a sense of "continually."

It sounds right. I think it's part of a TV commercial for diamonds.