If you are legally not required to file, you can state that and be in compliance and considered for financial aid. If legally required to file, but you haven’t yet, you will need to fill out the tax forms and then use those numbers in the Fasfa and CSS profiles. You won’t be able to do the IRS retrieval until you actually send your taxes in but that shouldn’t stop you from being considered for aid. The non-custodial parent will usually need to file as well.
If you file your taxes late, you will likely need to pay a fine and potentially interest on any tax due. It is unlikely there would be legal consequences unless you continue to avoid filing.