A best effort implementation should be fine. Advertisers already have suspected age fields available (derived from behavioral patterns, linked information across devices, etc). When you develop a reasonable suspicion that it's a minor then stop fleshing out the profile and targeting them. That's what the big players already do (maybe not Meta, but certainly at least Google). That doesn't quite fall into your (1) point since it's not profiling that's being banned, but profiling-based ads.