Assign configurable role to users over a certain age

It would be great, if in addition to checking whether a user is old enough to have an account, if the module could also have an optional feature to assign a role to users over a certain age.

That way, for instance, users who are over 18 (or 21, or whatever) could be assigned to a custom role, and then one of the many access permissions modules could be used to limit access to content that should not be seen by minors.