my dad in his early 70's has started shaving all the time, when he is going out somewhere he will shave twice within hours but denies doing this. He seems to constantly rub his chin looking for stubble then will go the bathroom and shave - he has never done this before, the hard part is that he denies doing this but we have found razors hidden in different places around the house and he gets very defensive if you mention anything to him. In all other ways he seems ok a little forgetful but nothing major. Is this change in behavior normal?
Whether it is dementia is much harder to say. Some kinds of dementia do involve obsessive compulsive behavior, but alone it is not enough to make a guess.
I suggest a thorough check-up by his PCP. Don't tell him it is because of the shaving -- it is just time to get a baseline established while he is well. Send a note to the doctor mentioning the shaving.
Regardless, confronting him or trying to convince him to do otherwise, may likely be futile. I'd certainly discuss it with his doctor though. Does his primary doctor see many seniors and dementia patients? Those who do and who regularly treat them, have more insight into behaviors that can be early symptoms.
He definately needs to see his Dr. Sending a note to the Dr. is a great idea and I'd like to suggest that you write on the note that the Dr. NOT come in and sit down and say, "So! You're shaving 5 times a day, huh??" I've sent notes to Dr.'s before and have had this happen and it just ruins everything.
If this is a bit of OCD, I wouldn't worry about it as this is quite minor.