years before 2020 are closed by the statute of limitations
assuming you are correct in that you can properly claim your son as a dependent (see below) you can file amended returns for 2020, 2021,2022
you did not reveal your filing status for those years
if you properly filed as single you can now file as head of household or
if you were married in those years and used the filing status of married filing separately (MFS), then you may be able to change to head of household filing status [probably more beneficial than (MFS)] if you lived apart from your spouse for the last 6 months of each tax year and also for each tax year you paid more than 1/2 the cost of maintaining the household for you and your son, who if married did not file a joint return with his spouse, and who lived with you for at more than 6 months in each tax year.
to be able to claim your son as a dependent
1. you can not be eligible to be claimed as a dependent by someone else
2. your son must be a US citizen, US resident alien, US national or a resident of Canada or Mexico
you can claim him as a qualifying child if all these tests are met
• he has the same principal abode as you for more than ½ the tax year. Temporary absences like for school are ignored
• if he is not a full-time student, he's under 19 at the end of the tax year. If a full-time student, he's under 24 at the end of the tax year.
• he hasn't provided over ½ his own support
• he didn't file a joint return unless there was no tax liability but merely filing jointly to facilitate a refund of taxes withheld or estimates paid
or you can claim him as a qualifying relative if all these tests are met
• his gross income for 2022 less than $4,400 (less in 2022 and 2021)
• you provided over ½ his support
• he isn't a qualifying child of another taxpayer
support
- Includes amounts spent for food, lodging, clothing, education, medical and dental expenses, recreation, transportation and other necessities
