I'm no expert on geese, but I think they will keep laying as long as they live. With that being said the amount they lay will decrease.

Somewhere in my home library I have a small book on Geese and it states that a lot of common barnyard fowl are amazingly long lived. I don't know how accurate it is (I don't even know where the book is now!) but I remember a story about a goose being trampled and killed by a horse while she was sitting on a nest of eggs that all eventually hatched in an incubator and that bird was over a hundred years old!!!! (I think it said she was like 110!) The authors stance was that there are few accurate records for farm stock and that a lot of ducks and geese are kept in flocks and no one knows how old they are.

I've seen some old geese in my life and they really showed their age after 12 years. I don't see how they could make it past 30.

20-25 is a decent age for a goose. 30 is pushing it but not unheard of. The ones that make it to adulthood quickly find out that ponds are their best protection from predators.