Prime age for race horses

Question
We are thinking of buying my 88 year old father a share in a race horse for a year.  I know absolutely nothing about horse racing so can you tell me what is the prime age for a race horse?

Answer
hi  well there is a lot of purse money for 2 yr olds, so people have a tendency to buy 2 yr olds to race, but a 2 yr old  comes up with a lot of problems, so a 3 yr old ---4 yr old  would be a better choice as they are already broken in and racing.  hope this helps you   thanks ED HESS