Each proposal carries a toggle that makes the client date of birth optional.
Turn it on and your customer can complete the proposal and pay without entering a date of birth. You set the passenger age type yourself on the proposal, so pricing still lands on the right fare.
Leave the toggle off and the date of birth works as it does on every other proposal, with the age type calculated from the date entered.
This helps agencies selling itineraries where the date of birth is not needed to ticket, and it keeps a customer from stalling at checkout over a field the trip does not require.