I think people do become more entrenched in their views as they become elderly.
One theory on learning that I found very useful was this:
You have a 'jigsaw' picture of a topic and also the world around you built up on past knowledge, experiences and the views of others (especially family, parents, close friends).
When you gain a new 'piece' it's simple to slot that in - if it agrees with your 'jigsaw'. If it doesn't agree, however, it requires a monumental effort of rearrangement (maybe a dismantling and rebuilding) of your entire jigsaw and you may have an entirely different picture! Many people will resist this great effort and just reject the new piece, despite logic and sound evidence!
Perhaps the elderly are just too tired to attempt the task of a change of view and are more likely to be deniers.