Can you live in a state for 6 months and be considered a resident?

It depends on what, precisely, you mean.

How residency is determined depends on what you're using it for. Normally it's defined as where your primary residence (again, exactly how that's defined varies) is. For tax purposes, if your primary residence was within a given state for any portion of a year, you can claim residency for that year (residents and part-year residents often have different tax rules than non-residents).

For college tuition purposes, normally your residency is determined by where you and/or your parents pay taxes. If you move to a state specifically to attend a school in that state, you are not considered a resident, but if you move to a state, take a job there, and then begin attending school, you probably are considered a resident.