Addon:BirthdaysGramplet
This gramplet will display the upcoming birthdays for the N next days. You can choose N between 0 (only today's birthdays) and 365 (birthdays for the whole year). A value like 7 (1 week), 15 (2 weeks) or 30 (1 month) is often a good choice.
Only the people who have no death event and, among those, only the people who are less than M years old are displayed (M can be chosen between 0 and 150).