The age 21 or older thing does not make a lot of sense. For college kids who are younger than 21, they can't include their parents' income? Then how can they get the income to pay the tuition (like $30,000 or so), room and board and daily expenses? And a lot of students get CCs anyhow.
This is really a gray area of the income from parents or from spouse. I personally do not think it is wrong to say that your 20-year old son makes $40,000 in order to get his CC. Or your spouse making $40,000 to get her first CC. The parents or husband (or other earners) pay the household debts anyhow. You can say the reported income is not true, but it is the reality.