In the late 30's and early 40's. The body metabolism slows down. You will find yourself putting on weight more easily. You also get tired more frequently. Therefore, taking supplements (vitamins etc), quality beauty treatment, good healthy diet, drinking plenty of water and sleep and is very important to slower the aging process. Of course, staying happy is an important issue as well.
If you can do all or most of the above, then make up is not an issue anymore.