If you have not done your taxes for previous years you can still have them done and claim the refund. But hurry you cannot claim refunds for taxes more than three years old.
If your spouse owes child support you don't need to pay for that, you can still receive the part of the refund than corresponds to you.
If you are a student and you are paying to go to school, you can claim your expenses.
If you work and you pay for babysitting you can use that to get more money back. In some cases child and dependent care expenses do not make a difference on the federal return but it will help get more money from the State.
If you are a homeowner and you also have a vacation home you can combine your mortgage interest and real estate taxes for both houses.
As long as you support your dependents it doesn't matter how old they are you can still claim them on your taxes.