Can a 19 year old attend a concert?

Yes.

Yes, I took my 9 year old last year.

Yep

Yes they mark you with wristbands to tell underage or not.

Yes. I took my 12 year old and his friend. $8 will but a soft drink in a cup that you can refill for free

I bring my 11 year old daughter if it's a kid friendly concert