Will they let an 18 year old in if it's to see a concert? Not looking to drink or anything, just seeing a concert

It is concert by concert basis. Usually the event listing on their website, the ticket page, and/or facebook event page will have that information.

You would need to contact the venue for information.

Some of their shows are 18+ some are 21 + and very rarely do they have all ages shows. It really depends on the event itself