30 wasn't old in the 60's. It was just that we were hearing a lot from college students, who didn't know any better and who thought 30 was old. Regardless of the year it is, it takes a human being about 25 years to have finished completely maturing, including the brain and skeleton. The trouble in the 60's was that kids who were 18 and 20 thought they could define "old" when Nature says otherwise.
I remember being in first grade and thinking the fourth-grade kids were old. Then in seventh grade I thought ninth-grade kids were all grown up. As a teen, I babysat for a young mother who was 23, and I thought she was "on the old side".
A lot of people just think anyone more than a couple of years older than they are are old. Then they get to that age and think the people just ahead of them are where the cut-off point for "old" is.
With more and more people living to be 100, I figure "elderly" is probably somewhere in the last 20/25 years of a possible 100-year life-span. (The first 25 years is a matter of reaching full maturity. The next 50 is living as a mature adult. The remaining 25 might be considered, "elderly"). Just my thoughts on "old".