<Tr> <Th> Northern Mariana Islands </Th> <Td>--</Td> <Td>--</Td> <Td>? </Td> <Td> 21? </Td> <Td> 21 </Td> </Tr> <Tr> <Th> Puerto Rico </Th> <Td>? </Td> <Td> 18 </Td> <Td> 18 </Td> <Td> Kept at 18 despite 10% highway funding penalty under Drinking Age Act . </Td> <Td> 18 </Td> </Tr> <Tr> <Th> Virgin Islands </Th> <Td>? </Td> <Td>? </Td> <Td>? </Td> <Td> 18 </Td> <Td> 18 </Td> </Tr> <Tr> <Th> Guam </Th> <Td>? </Td> <Td> 21? </Td> <Td> 18 </Td> <Td> 18 </Td> <Td> Raised to 21 in 2010 </Td> </Tr>

When was the federal drinking age changed to 21