Is Turbo Tax FREE FOR A 17 yr old STUDENT WHO Earned only $500 on a W-2?

If the 17 year old only have income from a W-2, then yes, they can use the free edition.  

However, unless taxes were withheld with income of only $500, they do not need to file a tax return as they would not have any taxable income since it is well below their standard deduction. 

If the child's W-2 does not have any tax withheld in boxes 2 or 17 of the W-2, they have no need to file a tax return, unless you just want them to get some practice in filling out a tax form.