I believe it'll display posts you've reacted to/made in the "Latest Activity" tab of your profile for only 1 or 2 months. After that, they start clearing out. Even when I go to your "Recent Activity" tab, I can't see more than you do.
You can still see posts you've made by clicking on your post count, but I believe reactions you've made to other people's posts will eventually disappear forever out of your timeline. The reaction left won't go away for course, but you won't be able to see them unless you happen to stumble upon an old post that you've reacted to.