Okay... here's my tale of 2 folks in their 60's who decided to try vaping. One if my roommate, and the other is my mom's boyfriend. They both were menthol light/ultra light smokers, but more than 2 packs a day each.
N., the roommate, tried it first since I, a former 2 pack a day of full flavored cigarettes, quit easily. So we got her the ego set-up and some 12mg menthol juice. Chokes, gags, sputters, says it's too strong. So she wanted to try other flavors, and I had a mild Turkish... so she ordered some in 8mg. Now, she seems to use it only when she's out or has the grandkids over, saying she wants something flavorless, since any flavor makes her hungry (remember, she was a menthol smoker). Okay, stalemate until we can buy some flavorless.
Now, my mom's boyfriend, M., has tried the cigalikes before. And I flaunted my ego set-up every chance I get. After months, he says he finally wants to give it his all, for the financial side of things (it does cost less per month, as long as you don't get mod-crazy). Okay, so I take over a spare battery, tank, and my roommates abandoned bottle of Menthol ejuice for him to try. I told him how to inhale and how to use the device, and pointed him to videos on Youtube as well. He chokes, gags, coughs and sputters. I told him he would, but he is taking it slow. I tried the menthol juice, and for me, it's quite mild. But neither of my 60 year olds seem to want to tolerate the full conversion.
M. always coughs and hacks a lot when smoking, too. He just has bad lungs. I think he's stubborn enough to get through the familiarity stage, but for the older folks (I am in my 40s), it seems harder for them to convert from my experiences.
So, give your Dad time to adjust, and offer him the support and guidance needed to get through the initial stages. We all know the benefits, but they might not want to proceed. Good luck.