@christianp Two friends of mine who were married for over ten years were born exactly one year apart (well, at least on the same day of the year, "exactly" is exaggerating, but sufficient for the parameters of the question) so there's your second-hand evidence.

Answering another question which isn't what you asked, but it's a logical follow-up question: my late husband was born four and a half years after me, so his birthday was my half-birthday and vice versa.