AP scores never expire. Once you have taken an AP Exam, your score is permanently stored on your College Board record. You can access your scores and send them to colleges at any time in the future, even years after you graduated from high school.
However, while the scores themselves do not expire, their relevance to college credit may change. Colleges periodically review and update their AP credit policies. A score that earned you credit five years ago might not earn you the same amount of credit today if the college has changed its policy. Therefore, it's always a good idea to check the current AP credit policy of the college you are sending your scores to. But rest assured, your hard-earned scores will always be a part of your academic record, ready to be used when you need them.