An average credit age of two years or less is considered poor under the scoring model, from what I've seen. (money.stackexchange.com)
One contributing factor to this could be the limited access to credit this age group faces. (valuepenguin.com)
However, be cautious with this approach: A new credit card can reduce the average age of your credit accounts and around 15 % of your credit score depends on credit age. (finder.com)