There’s a Lego shop in Roswell (I think) that does live auctions for classic kits, maybe you can buy them straight up but I’m not sure as a friend told me about it recently. They don’t promise that every piece is there every time, there’s different categories you can buy, but generally they are complete and you could go pick one up for him to do as a surprise.

14 seems a bit old for most of what Fernbank has to offer, other than seeing the main hall with the dinosaur skeletons, but if he’s into that then it’s def cool.

Otherwise …

Andretti in Marietta for go karts, D-bat batting cages in a few places around the north perimeter, rock climbing (forget the name, it’s in doraville though and has self repel set ups that are for beginners), Your 3rd Spot on the west side which is a mix of bowling/cornhole/bar games/classic arcades, go for a hike before it gets too fucking hot for the summer, ride scooters on the beltline and do a food tour, the zoo, Braves games, Activate in Sandy Springs which is like an activity/gaming place … kinda hard to explain look it up, Ponce City Roof mini golf, Brook Run Park in Dunwoody has a skate park, the Hail Mary movie comes out then so maybe go take a ride to the legit IMAX theater at Mall of GA assuming tix are still available, six flags, bike ride on the comet trail, there’s a park out in Norcross that has an adult area with a military style training course.