> The interpretation of existing jurisprudence is that age limits on the free exercise of rights is Constitutional in many circumstances regardless of if such limits are not explicitly in the Constitution.

This is explicitly the case with voting rights, but other than that? While there a contextual limits where age may be a factor as to whether the context applies (e.g., some of the linitations that are permitted in public schools), I can't think of any explicit Constitutional right where the courts have allowed application of a direct age limit to the right itself. Can you explain specifically what you are referring to here?

> I can't think of any explicit Constitutional right where the courts have allowed application of a direct age limit to the right itself.

Right to keep and bear arms -- federally 21 to buy a handgun and 18 to buy a rifle/shotgun from an FFL. Although sometimes you can touch federal law (NFA) and not have such limit -- a 12 year old could buy a machine gun or grenade for instance privately and still be able to buy a federal tax stamp.

Speech - a little looser but the 1A rights of minors in schools are a little bit less than that of staff. It's been awhile since I looked over the cases but IIRC staff had slightly stronger free speech regarding political speech than students (I'll try to dig up the case later if someone asks for it).