I have no idea what your intentions for this spell is whether it for beauty and youth or for other reasons but,
Think of it this way, (aside from all legal matter especially pertaining to appropriate sexual behaviours). Age is just a number and concept in your mind, and that number should not dictate your life. You should not be restricted by it.
Magic is the method of changing and influencing your surrounding but you start be changing internally which then is reflected outwardly.