Frank Lloyd Wright was considered washed up and done in his 30s after a successful period. Most of his greatest works came late in his life. The Guggenheim museum, just as an example, was designed just before his death.

Ray Kroc was already in his 50s when he bought out McDonalds and turned it into the success we know of now.

The point of seizing the moment is to make the most of right now, not make you feel guilty about the past.