User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-5938567-20130113181814/@comment-3146930-20130201210531

Sure he can. While the Fates have vast knowledge of future events, the future is always changing and many events involve a choice. Percy saw his future after Luke killed himself to save Olympus, but Luke could have also destroyed Olympus. In other words, Percy saw a possible future of himself growing old, but not the definitive future.