You should know roughly 2000 kanji once you pass high school.
Maybe 3000 kanji to get through university, unless you are a student of classical Japanese or Chinese literature, then maybe 5000+.
Nowadays people rely on the keyboard and the iphone to complete the kanji, so while most Japanese can recognize 2000 kanji, they may not be able to actually write 2000 kanji (kind of like people in the US know the word schizophrenic, but might not be able to spell it accurately).
Older people may have a slightly high advantage when writing, because their generation did not allow them to use computer crutches like auto-complete or auto-select. So older people may actually be able to write more random kanji than younger people.