By way of corroboration, a paraphrase from Confucius:
- When I was fifteen I set myself to study.
- At thirty I knew where to stand.
- At forty I was no longer confused.
- At fifty I was able to follow the will of Heaven.
- At sixty I could hear anything with equanimity.
- At seventy I was able to do anything I liked without violating moral principles.
A more flippant observation from some quote server: It takes about ten years to get used to how old you are.