The fact that they're both elderly is kind of a coincidence. It is true that older candidates are the ones with the longest track record of accomplishments and the most extensive alliances.

But the GOP candidate had little government experience and somewhat dubious business experience. He is nonetheless popular for his style and positions.

Both parties are very diverse and it's difficult to find someone tolerable to all. Many actively despise their party's candidate but the alternative to the consensus risks losing entirely. It is generally thought to be better to vote for a suboptimal candidate than a pessimal one, though some vocally disagree.

A young, charismatic candidate could come up next time around, but to be honest neither party seems to have one getting ready.