If someone is trying to defraud someone whether in business or looking for a shidduch, by dyeing the hair to appear younger, it would seem to be assur. But many young men go gray prematurely. Why should a 30 year old man feel uncomfortable around people, just by virtue of having gone gray 20 years sooner than most? And if he is not married, it can be a real hindrance. And why should someone in the workforce have to compete with younger-looking men, in a place where youth and vitality are prized, and age is devalued?
These are issues that were not as prevalent centuries ago. If someone dyed his hair, it often was for arayos of some type, or Avoda Zara. Not so, today. People just do not want to feel old. A more youthful appearance helps.