As an admin, you have several options:
1) You can create Buy Items (there is a Buy item image for donations) for Sponsorships and add them to a Store page or as options during your Registration process.
2) You can add Sponsorship Levels to your existing "Youth" Program -- at the bottom of the program '2 Configurations' page. In this scenario the Program "Offerings" are still the different age groups and the Cart page adds an "Enrollment Selection" drop down for the different Sponsorship Levels you created.
3) You can create an "Adult" Registration Program specifically for the Sponsorships. In this scenario the Program "Offerings" would be the different sponsorship levels.