If i had a non contrast mri a ct, 3 routine normal eeg, should i still be concerned about my deja vu spells being seizures? can / would they typically start at age 20? thanks?

Yes, epilepsy does commence in adolescence and early 20's. Deja vu episodes can be associated with complex partial seizures, but also some psychiatric conditions, and even migraine on occasion. Standard EEG's often miss cerebral activity due to the short time interval. An ambulatory EEG lasting 72-96 hrs would capture far more activity. Discuss your next steps with your neurologist.

Yes and yes. Those tests aren't the patient; you are. The astute clinician knows when to trust and when not to trust test results. More prolonged EEG monitoring, either inpatient or outpatient, would be my next step, but I'm not your doctor.