Found some more info in staff travel manual. More than 10 years of service and less than 50y old, you get zip. As I understand, with more than 15 years of service, regardless of age you get similar benefits as with the +10 years service and within 10 years of retirement. In short, if you join when you're less than 35 you're in a disadvantage if you leave between 10 and 15 years of service.