He could retire when you’re at the height of your career
A woman in her forties or fifties is often at the height of her career. This can be when she’s earned the most respect, money, status, and notoriety. This can also be when she has to work the longest hours, take the most meetings and go on the most work trips. Meanwhile, if her partner is in his seventies or eighties he may be retired, leaving him spending his retirement alone.