I don't see how a scheme where you allow the generation of multiple tokens will be practical when the token itself has value decoupled from the concerns of the generator - such as when the token doesn't give access to your personal account.

If the token signifies you are 18+ and nothing else and if the generation limits are such as to be reasonable then people will generate some fraction of their total tokens just to sell them, or use their elderly relative's tokens.

The kids will be trading these tokens to each other in no time. Token marketplaces will emerge. The 18+ function of the token will just become a money/value carrier.

If you limit it to one token per person, the privacy implications will be devastating. All online presence where being 18+ is required will be linked.