Agreed. A better way would do it demographically which would look at where the ‘boom’ and the birthrate dropped.
1945-1960 is probably a better ‘boom’ and 1960-75 better for generation X if you are defining it by the change in birthrates.
Contrary to what many believe, the echo in 1990 was the highest it had been since 1972. Most of the birthrate since had dropped.
So that would make it 1945-60, 60-75 and 1975-90.
Even the trough of the great depression, more kids were born than in the ‘echo’.