"The glory of young men is their strength, and the honor of old men is their gray hair"
Solomon is here trying to show the different strengths of people at various ages. The young person is highly valued because of their strength and vigor. The older person is valued for their gray hair; for having survived the various challenges that life throws their way. In that day only those who had some level of wisdom grew old enough to get a head of gray hair.
This was Solomon's way of saying that one of the most valuable things about older people is that they have been around and have probably seen people take various roads and try various ideas. It is their experiences that make them valuable or give them the honor. It is these experiences that are reflected in their gray hair. They can say: Oh, I tried that in my marriage; don't do that. Or, I went down that path financially; that is the best way. Or in business one needs to watch out for people who do this and such.
strength
This is the Hebrew word koah which means strength, power, ability, might, force, energy. The idea being not that all young people are physically strong; it is that they have a much higher level of energy and effort that they can bring to a project. It is this energy that makes up for their lack of experience in many cases.
On the other side, the older person has experience so they do not need as much raw energy. They are usually smart enough to not go down dead ends.
In our day and age, many people are able to survive to older ages without the wisdom that was required in those days. One must not just live a long time. but one must learn during the journey. One should also produce a righteous result in the process. There will be a day when we must present our soul to the Lord -- what we deposited in it and what we used our life for. Will it be wisdom or folly?
Until tomorrow,
Gil Stieglitz