He wasn't past his prime, he was just entering it. Ageing is a kindness. The young person is too easily caught up with his body and with material goals. The ageing process reminds him that he isn't going to live forever, and that only spiritual accomplishments are going to accompany him to the next world. He is reminded to increase his study of Torah and his fulfillment of mitzvos, things that he can take with him.
Spiritual accomplishments increase with added age.
The Torah does not consider the elderly person to be a fogey or a fuddy-duddy. He has seen the best of times and the worst of times, and these afford him a uniquely broad perspective on things. Armed with the wisdom of experience, focused on spiritual pursuits, the zaken is able to work towards the next stage of his life. It has been noted that there are many parallels between death and marriage. We already noted that the laws of kiddushin are learned from the purchase of a burial plot.