Yeah i'm new to the game and i have to say I noticed the same. My King is an old geezer of 75 and recently he still had a child with a woman in her twenties. So yeah those old fellows are still 'active'. Which is good if by misfortune you are out of heirs, you still get the of chance he'll get lucky at an old age
EDIT - few years forward and he's added I think 2 more if memory serves me. Heck he's lived VERY long. Heir nr2 even died at a ripe old age already...