When is the best age?

Probably 21. When you turn 21 you are just beginning to understand what adulthood means. You are no longer a child, teen, but you are then an adult. At 21 you not only get your full license, but you have so many privileges. Even though your responsibility increases you get a chance to feel your way into adulthood. Its kind of like the prime of your life. I would say from this age until 30 is the best time to live. But then again ages don't really matter in this argument, because all that matters is what you do with your life. You can be 21 or 12 and if you aren't making good use of your time then you won't benefit from it. I guess my answer is in two parts.

Every age has its pros and cons. I don't think there is a "best age."

I'd say 18.