Well Sir, I think you need to understand a little more about getting older and the mindset of the generation you are dealing with. I liken the aging process to the loss of your comfort zone. I work with seniors everyday, and they can become cranky. I am guessing not unlike when your favorite band from your youth became classic rock. As far as senile dementia, it is hard to tell without more information. Dementia is a collection of at least two symptoms, with one of them being memory loss, stubborn not so much. Also you should know that dementia and depression are not normal parts of aging.
I would give a little space to see if the "problem" comes to the surface. If you were to feel that there are signs of dementia or depression, seek professional help. Last remember that you are still the child, or married to the child, and children are to be seen and not heard. That's that generational thing again.