Perfect age for the parent or the child?
I agree with the above... there is no "perfect" age. It all depends on when the parent is ready, and what type of challenge the parent is ready for.
There are minimum and maximum adoption ages. It depends on the adoption agency and state laws. International adoption requirements also differ - in order to bring home a foreign-born child, the adoptive parent must be at least 25 years old if single. For Chinese adoption, the adoptive parents (must be married at least two years - man and woman) may be no younger than 30 and no older than 50 (55 for couples adopting special needs children). For South Korea, the adoptive parents must be between 25 and 44 years of age (must be married - man and woman - for at least six years and the couple must be within 15 years of eachother in age).
Most foreign countries require the adoptive parents to be married for so long (and if there has been a divorce, the marriage requirement is even longer), but not all. As for domestic adoption, I know that Mississippi requires the adoptive parents to be married and Florida doesn't allow homosexual parents to adopt.
No matter where you're adopting from or when you're adopting, it is important that you are financially capable of raising a child, as well as able to be at home with the child in the evenings.
[China has very strict adoption policies, and the minimum overall family income is $80,000 per year with at least $10,000 for each person]