Lazy eyes can be cured though you are 21 years old. We must know that we can retrain our brain. The developmental optometrists can make two eyes to work as a team. The first thing you need to do is to have a functional vision test, this will help determine the extent of your vision problem. Then, you need to find the right lens or glasses. The right prescription at this time can restraint the stronger eye to bully the weaker eye. Meantime, you need to take serious visual activities. I suggest you to look for patching and vision therapy. Consult more information from your eye doctor immediately. Good luck!