The problem with the US federal government making "sex" laws that applies to all 50 states is simply that they don't have the authority under the US constitution. In the cases of foreign or interstate travel, and on federal land, they do have clear laws. The federal age of consent is 18. I do not believe that federal law has an age difference exemption, thus, if you and your bf can legally have sex in your state, but you go to a national park within that state (assuming you are both under 18) and have sex while camping, you could both be arrested and face federal charges. If you are an adult and cross state lines to have sex with a minor, or facilitate a minor to cross state lines to have (otherwise legal) sex with you, you have violated federal law.
If the federal government were able to regulate sex laws, they would have carte blanch to make similar regulations for anything within the states, and this would totally invalidate the reasons for having states in the first place, and the "federal" form of government. Since (unlike the former Soviet Union) there is no provision for a state to secede from the Union, the removal of the ability to create their own laws would create the identical circumstances that lead to the Civil War.
Just like you can go to the grocery store and choose your brand of bread, soda, and potato chips, you have equal freedom to move to a state that has laws more suited to your personal beliefs. That is something I would rather never see changed, even if it means you have to keep track of which states you have to wear your seat belt in, and which ones you don't.
:king: Dr. Mr. Snow "Snoopy" Dog