Harry Potter was born in 1980.
According to the Harry Potter Wiki, it stats that Dolores Umbridge was born, at the latest, in 1976, but was born sometime in the 1970s. At the outside of the range, born in 1970, she's 10 years older than Harry Potter. At the inside, she's 4 years older than he is.
Is she really under thirty? If so, is there any particular reason she looks older? (Imelda Staunton, who plays her, was born in 1956.) And how is she so far into her career if she's really that young at the time?
EDIT: At this point, there is no reference to an actual birth year for Umbridge. Knowing the nature of a wiki, at the time I asked this question, I should have included a screenshot to show the birth date information as it was at the time.