Yup. I’ve gotten criticized on the DIS for posting about this in the past, but DS11 and I often visit various WDW lounges (who has time to mess with ADRs?) and sat at the Dahlia bar last November. We had a great time and the food was excellent. I always tip extra since I’m with someone that’s not necesssirly contributing all that much to the bill, but that’s just my personal choice.
The only true age restricted place at WDW off the top of my head is Trader Sam’s at Poly after 8pm. Also perhaps places like Jellyrolls or Atlantic Dance Hall. But otherwise, no worries at all.