My Dad would have been in his early 30s in 1967, in a managerial job, and he never, ever had long hair. He did use Brylcreem, though. Terrible stuff! No wonder people used to have antimacassars to protect the backs of sofas and armchairs from the greasy marks.
My husband was in the early years of secondary school at that time. His memory is that hair length was a big issue at school all through the late 60s and early 70s, with boys being sent home if their hair was longer than deemed acceptable. Hair below collar length started to get more and more common, though, to the point that short back and sides stood out as old-fashioned and fuddy duddy in the 1970s. Really long hair on men was very common by the very early 70s, and then started to look old-fashioned in just a few years, with the rise of punk and then the New Romantics.
This old Pathe newsreel clip of London street scenes in 1967 is good fun, if you have just under 8 minutes to spare.