Age is sort of a factor, but it's mostly income.
Unfortunately, it's not simple to answer the question Who Must File. I've attached two tables from IRS Pub 17.
If someone is claiming you as a dependent look at Who Must File - Dependent (below)
If no one is claiming you as a dependent look at Who Must File (below)
If you have
W2 income and there was
withholding the only way for you to
get your withholding refunded is to file a tax return.
