Best age in my life was probably around 15-16 years old. That was the point in my life where I resolved a lot of my personal issues and where a lot of other crap in my life ended. Currently 19 years old.
I don't buy into golden age fallacies.
I agree, if you mean that a certain age is the "golden age." Everyone has their ups and downs, and if you look at it objectively, you're going to have years that are better than others and the reverse. Out of those, one or two would definitely come to mind as "the best."