What age would you be if you could turn back the clock and why?

If I could turn back time, I would go back to being 21 again. My youngest child would be a newborn and my oldest child would be two and a half. At that point in life, I could watch them grow up again -- as nothing is better than watching children learn and experience life. Hopefully, I could take my maturity with me when the clock was turned back so that I could enjoy the process more instead of stressing out over the little things.