It was a guess, and qualified as being highly improbable. It is a fact, though, that Downs can be due to the father’s age.
Another possibility is that it is inherited, as a minuscule number of Downs cases are, and we just haven’t noticed it since it is very rare and we don’t test everyone as a matter of course. If so, it would most probably be recessive, since the parents of the two people were obviously fine.
Best you read this ;-) [ maternal age is the linkage ]
Other articles point out that older men with older wives share the risk, but not older men with younger wives.
NET: women over 35 who are pregnant and want to know should get the pre-natal exam.
Full disclosure: I was a physiology major years ago (very close to pre-med curriculum) and have two kids who work in healthcare, PLUS I serve the healthcare industry in my professional role.