I ate my first eighth of mushrooms on my 15th birthday, before I tried smoking marijuana, after an initial curiosity of those realms. the opportunity arose, and so i took it. the experience didn't harm me in any way, no regrets at all, but i must say that i get a lot more out of psychedelics now that i'm older, and have more life experience and knowledge. however, since i tripped out my first time in my mid-teens, i viewed reality in a more psychedelic light earlier than my peers. i feel that i saw through a lot of the superficial bullshit of high school social situations, and held a higher interest in more metaphysical and philosophical areas (i must state that it took a bit of time to get used to how "different" i felt from my classmates - not everyone responds well to isolation from peers). my initial interest in psychedelia has blossomed in to something very spiritually fulfilling, through developing a relationship with myself and the universe. i feel that psychedelics have allowed me to tap in to wisdom beyond my years on the earth, and I'm very grateful for that.
That is not what happens for everyone, but it has been my experience. I'm not going to say whether a person should trip at this or that age, as everything is relative to experience. I will advise though, that waiting until you know in your heart and your gut that this is what you want. Know what you're getting in to, read about drugs in general for a while, think about this decision. psychedelics are always around if you are looking, so there's no need to rush things. you know what they say, once you trip, the world is never the same. and although there's no way of preparing yourself entirely for the descent into the rabbit hole, it really helps to be educated on the subject. In the end, it's your brain, and you only have one, so be kind to it. if you feel apprehensive about taking drugs, wait until you feel comfortable with the decision, it will be more worthwhile in the end...
stay curious, and know yourself by whatever means you choose =)