I don't see dates of birth for either of them showing on their profiles, but he was married multiple times and it's not unheard of for older men to have married younger wives in hopes they'd produce more children. My son has one ancestor who married women much younger when he was in his 80s and produced more children.
Anyway, I found one site that says Mary was born abt. 1373 but most don't list any dates for her other than when she and Thomas married.
http://venitap.com/Genealogy/WebCards/ps44/ps44_377.html