Or use the same explanation that was used in pre-crisis/post-crisis times, that the JSA ages slower thanks to Ian Kargul's demise and other factors. It certainly happenend on this Earth 2 as well. This could also explain why their children age slower. Throw in superpowers and it works in any case.

Then again, Earth 2 could still be caught in the 80ties. It is possible, with Mr. Mind damaging the timestreams. One of the Earth is still in the 19th century, Ray Palmer spend five years on Earth 50, with only a fraction of that time passing on New Earth.
So at the moment anything goes.