There are pros and cons for either demographic: whilst being older may be ideal since not only you bypass age restrictions, you also have the capability on purchasing it with your own money without having to ask parents for that given that you have employment and recurring income. Gaming as a kid gives more time without having to dwell much on responsibilities that adults have to worry about but at the same time are held by school.
As you said, there are pros and cons. A child’s brain is something else, I remember excitement and curiosity that an adult’s brain just cannot replicate. I don’t think I’ll ever feel what I felt when I played Half-Life or World of Warcraft for the first time. Games are still enjoyable though - just in a different way.