It never happened...

[comsol]

2) it's revealed that while Kal-el has been travelling from the same point in the past, he's been visiting the legion across many decades in the future, rather than being young adults, they are all in their 60s and 70s but due to anti-aging drugs have not aged. For complex plot reasons, Superboy must never know this.

As I recall, the Legion members were only in their twenties (although Superboy still thought that they were teenagers), not in their sixties or so. Unfortunately the thing that I remember most from that story was how badly Vince Colleta's inking screwed up Mike Grell's artwork.

 

[RJDiogenes]

Poor Vince Coletta. The only artist he didn't screw up completely was George Tuska.