Went to my first horse show when I was 4 years old (halter classes, western pleasure, and gaming barrels & poles).
Took my first official riding lesson at age 25, and have taken a lesson here and there for various disciplines.
So I guess you could say I took the "back way" to riding, because I just plain grew up doing it. You are certainly never too old for riding lessons though! You can always learn new things.
Maybe for some persceptive, I have a younger cousin who started taking riding lessons probably about 4 or 5 years ago. And I believe last year was when she competed in her first schooling show. She does not have her own horse, so she uses her trainer's horse. I just watched her compete at a show this past weekend and each event was $10 (she did 5 events), plus the trainer charges $75 for the day to use her horse and for coaching, plus her mom and dad drove 3 hours one way to the show (gas $$$), please you buy food to eat while you are there, etc etc. They said for the whole weekend, they were spending about $300 when it was all said and done --- and that was without overnight stalls.