Hello! Two very different questions here. I cannot answer about taxes, but I CAN confidently answer about the FAFSA (I worked in a college Financial Aid office for 6 years).
While the FAFSA does look at taxes in determining eligibility, a student is considered to be DEPENDENT (meaning they have to use their parent(s) tax information whether they want to or not) until one of several things happen. 1.) They turn 24 (NOT 22...it's 24) by Dec 31st of the award year, OR 2.) they have a child they support, OR 3.) they are a veteran, OR 4.) they are an orphan/ward of the court, OR 5.) they are married, OR 6.) they have a dependent (other than a child) who they support (roommates and boyfriends don't count...and yes, I've seen people try that one on their FAFSAs before). :)
Whether the parents claim the college student on their taxes or not, the student must still use parent tax information on their FAFSA until one of those above criteria are met. It was not uncommon at all for 'dependent' students to not be listed on their parent's taxes. By the way 'dependent' and 'independent' are the official terms used by the government with financial aid.
In the 6 years that I worked at this financial aid office at a very reputable 4 year college, I can only think of maybe a handful of situations which we were legally allowed to change a student from Dependent to Independent. As in it is almost impossible to do.
SO, plan on having your financial information listed on your child's FAFSA for a while.
Other note: The FAFSA is set up in such a way that they are using the previous year's data as a predictor on what a family can contribute in the upcoming year (whether or not the family actually contributes at all doesn't matter). *IF* you had a situation last year that makes your income look significantly higher than you anticipate it to look in this upcoming year, you can file paperwork for a Professional Judgement to have your income (for FAFSA purposes...not tax purposes) adjusted. For example say you or your husband lost their job recently, but last year's taxes would show two incomes...this would potentially be grounds for a Professional Judgement, and you could talk with a financial aid counselor to help you navigate this process.
Otherwise, plan on DEPENDENT for the status (whether you plan on helping your child or not).
Last thing...While the FAFSA can be filled out just about any time, there ARE priority deadlines that can make a difference in eligibility for limited funded items. If you think that your child will have any grant eligibility, then I would strongly encourage you to get your taxes done ASAP and get the FAFSA submitted online ASAP. Some aid is guaranteed if you are eligible. Other aid is on a first-come-first-served-IF-you're-eligible basis. When I worked in this office, the difference between a Feb 15th FAFSA submission date and a March 15th FAFSA submission date could potentially be the difference of about $3000 in grant eligibility. NOTE: Pell grant funds don't run out, so I am talking about other grants here. Loan eligibility will always be there, as well.
Go to fafsa.ed.gov to fill out the paperwork. :)
ETA to Julie S: Yes, that is one thing that I forgot to mention. The dependent vs independent status will also change once a first bachelor's degree is completed (they have several very small loopholes, and that is one of them!). :) That is why Julie's daughter was able to switch to Independent status for her Master's degree, but before turning 24. Also, in case any of you are curious, any GRANT eligibility no longer exists after a first bachelor's degree is completed. SO...if your child is working on a double major and they have grant eligibility, make sure to have them finish both degrees in the same semester, or they will lose any potential grant eligibility after the first bachelor's degree is awarded. Probably not surprisingly, LOAN amount eligibility actually increases for a 'graduate' level student. Fun stuff...student loans... ;)
Ah, all the ins and outs of this process. Sigh. :)