Bear in mind that when the constution was written, there were several huge cans of worms left completely undisturbed because those issues were simply too devisive: slavery of course was number one on the list pitting North vs South. Others were the status of debts owed to foreign companies incurred before the revolution, Indian affairs, alcohol (abolition or management), land policy and a host of others.
The issues tended to be more of local than national interest. eg. Land policy was a no brainer in original 13 colonies but how do you handle it in newer territories like those gained by the Louisannia Purchase or the far West? The Indian nations in the east, the so called civilized tribes were a sedate lot. The plaines indians and those further west however were quite fierce. Eastern states were generally apathetic about indian affairs but to the territories, it was a matter of life and death.
These were issues on which no national consensus could be reached and were handed off to the various states for the most part. States weren't given carte blanch to do just anything they wanted.
The early supreme court spent a great deal of its time defining the limits and bounds of both federal and state powers.
Some of these matters were returned to the Fed by the Court. In 1812 Congress created the General Land Office which eventually became the Bureau of Land Management. In 1824 the Bureau of Indian Affairs was created to curb graft and corruption in dealing with the independent tribes by oppertunists in the territories.
Other powers were returned to the states- like the imposition of various taxes, the granting of franchises and licenses , etc.
Point being: historically these powers have been shifted from state to federal levels and vice versa typically after one or both of those entities had royally screwed it up.
A good case could be made for a national age of consent: as it stands now, it is confusing, contradictory and so uneven from state to state that the issue begs for oversight. This is not something that can be done by congress alone. It would involve a supreme court decision followed by congressional action. Last but not least, the state laws that we seek to superceed have to be proven discrimitory or unconstutional and struck down.
I would suspect the the broadest type comprimise would be made where the federally recognized age of adulthood is defined as 18 with 16 being the age of consent for partners 3 years.
Nothing radical but some states would raise hell over it.