I know that this is not what you want to hear, but when you are talking averages not specific people, there is a measurable decline in ability for all sorts of reasons to learn new skills. Hence the maximum age to enter military and civil sponsored flying training was about 26-27 years. Older people develop inhibitions, are less likely to accept instructions to "do this" and usually find concentrated study a bit more difficult than when they were 17 years old. But hey, if it's what you want to do, go for it.