Equinox and Leap Year

Grau and I have had discussions in the past about the first day of Spring. He said it always falls on his father's birthday and I said that can't be because sometimes it falls on my father's birthday (both gentlemen were born in March two years apart).

Fast forward a few weeks and suddenly it's March...wow how time flies.
And I wondered yet again, how it is that I remember the first day of Spring being on my father's birthday, but it hasn't been for a few years.
So I looked up Vernal Equinox.

And a friend posted about the equinox (which, for those of you wanting to know, actually means "equal night") and how it snuck up on her this year. And I posed the question to her- how could the equinox be on the 21st every four years but not have been on the 21st for the past five?