My Hindu monarch has the Brahmacharya -100% chance for a new heir modifier, but he still got a 0 age heir. Did the Maharajah forget his vow to Vishnu, or is it a bug?
4 royal marriages, that's what did it alright..Is Heir chance additive? You may have had a +heir chance modifier from something else that meant you still had a small chance of an heir. Did you have any royal marriages?