I never received any stimulus funds in 2020. I am 17, a student, and worked, so my income is well under the limit. Why can't I claim it on my return?

We can't see your tax return however per IRS Recovery Rebate Credit — Topic B: Eligibility:

If you cannot be claimed as a dependent on someone else’s return for the 2020 tax year, you may be eligible to claim the Recovery Rebate Credit if all other eligibility requirements are met. 

• See How do I claim the Recovery Rebate Credit in TurboTax?

You are not eligible for the Recovery Rebate Credit if any of the following applies:

• You may be claimed as a dependent on another taxpayer’s 2020 return (for example, a child or student who may be claimed on a parent’s return or a dependent parent who may be claimed on an adult child’s return).

For additional information, see How will the second stimulus impact me?

[Edited 2/24/2021|5:19 am PST]

The simple answer is: 17 year olds don't get the stimulus because they can still be claimed as a dependent by their parent regardless of how much work income they had.

Under the CARES Act, if you are claimed, or qualify to be claimed, as a dependent on someone else’s 2019 return you cannot receive a stimulus check, in 2020.   If you qualified as a dependent for 2019, but will not be for 2020, you will most likely get it in 2021, when you file a 2020 tax return.

Note that the requirement is not just whether you are actually claimed as a dependent, it's whether you qualify to be claimed as a dependent. 

There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test.

A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:

1. He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
2. He did not provide more than 1/2 his own support. Scholarships are excluded from the support calculation
3. He lived with the parent (including temporary absences such as away at school) for more than half the year

So, it doesn't matter how much he earned. What matters is how much he spent on support. Money he put into savings does not count as support he spent on him self.

The support value of the home, provided by the parent, is the fair market rental value of the home plus utilities & other expenses divided by the number of occupants.

The IRS has a worksheet that can be used to help with the support calculation. See: http://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf

Furthermore, there is a rule that says IF somebody else CAN claim him as a dependent, he is not allowed to claim himself. If he has sufficient income (usually more than $12,400), he can & should still file taxes. In TurboTax, he indicates that somebody else can claim him as a dependent, at the personal information section.  TT will check that box on form 1040.

Even if he had less, he is allowed to file if he needs to get back income tax withholding. He cannot get back social security or Medicare tax withholding.