Richard Graves' term would've been during Reagan's second term and George HW Bush's only term. Neither are ever mentioned in the series so it's unknown if they even exist in this universe.
First two episodes streaming on Crackle early before the October premier date on Epix.
Maggie and Richard's ages are never given in the series, but assuming they are the same age as Nick Nolte and Sela Ward then Richard would have been 43 when he became president and Maggie would have been 28 when she became First Lady. This would make Richard the second youngest person elected President, he'd have been a few months older than Kennedy. And Maggie the second youngest First Lady after Frances Cleveland who was 21 when becoming First Lady.
There has never been a president from New Mexico. In fact there has never been a president from a state primarily in the mountain time zone.