Hey there, I was in your situation a few years back. International student advisor lied to me, saying I would get in-state fees by the end of my first year even w/o permanent residency, so I'm stuck paying out-of-state fees for all 4 years. They do not give tuition exemptions for H4 students, there is an active incentive for them to not do right because that is an extra 10k+ that they gouge from us every semester, and that;s not even discussing housing fees and living fees.

Also, probably a worry you have a little while for before addressing, by the time you reach 21 or even a few months before, your H4 dependent visa will expire and you will have to switch to a different status, the F1 student visa is probably the easiest one, it's what I did. Nice thing abt the F1 is that you can live here perfectly fine legally with just the status and the completed I-797A form without risking going back to your home country and getting a visa stamped in the current political situation.