I'm not surprised that at 77 he refuses to quit! The older we get, the harder it is to make a change of any kind. Tread lightly, have it available and let it be at his pace and with his input! Even if it replaces 5 cigarettes a day for him, it is a victory.
The flavoring is key I think. If he doesn't enjoy the taste, it isn't going to be something he'll even use enough to give
vaping a fair shake.
Prefilled cartomizer flavor isn't for everyone (I can't take them either, and I'm not 77! *grin*). Perhaps filling cartomizers yourself is a better idea for him? The tobacco flavors are best for beginners, and a good non sweet flavor such as Heavy Shag/Cigar seems to work well. Watch for
reviews on ECF for tobacco liquids:
E-Liquid Reviews - E-Cigarette Forum
Does he enjoy coffee? The Café Sumatra from VaporStation is divine (and the only coffee flavor I've found that is truly good and not perfumy or chemical tasting... I can recommend most all his flavors with the exception of the wood smoke flavors as being great without the perfume and chemical taste in most imported liquids. His are from India).
RY4 has a sweet caramel flavor with a tobacco and is a favorite for most beginners and long time users alike. If he has a sweet tooth he might enjoy that also. Find a few samples or look on the Classifieds for inexpensive bottles from other members to purchase. There also is a liquid exchange social group on ECF that you could join.
The coughing is probably one of two things, though most of us cough a little the first few days. If he is drawing the vapor directly into his lungs (a common new user error) direct him to hold the vapor in his mouth first and then slowly draw into his lungs.
The coughing could be caused from a reaction to the PG in the liquid which is common for a small percentage of new users. There are several companies that sell 100% Vegetable Glycerine liquid on ECF, so that would be worth trying. Even a 50/50 mix of PG/VG could ease the coughing and associated throat irritations that many find with PG.
Keep a selection of medium and high nicotine strengths around. Higher for when he really wants a cigarette is good... 24mg might be the ticket to start him off with. If he takes to the e-cig, you can cut it back later.
I think you are spot on with the idea of cartomizers for him. You could fill enough for a week for him so he has little effort except to pick it up

.
While I didn't care for the vapor or flavor of the KR808 (or even how the blanks performed with vapor) I've recently tried the blank 510 cartomizers and like them very much. I found them to have very good vapor and translate what ever flavor I use well. Look for the ones that have the removable tops since that makes them easier to fill up. The hard tops aren't easy to remove and I fill them through the battery side with the silicone cap fill method. The 510 cartos will work with all 510 batteries and you can buy adapters for other KR808 batteries if you have those already (KR808 to 510).
Drew at NHaler has the mega size 510 cartomizers. Might be worth trying for him since they are a larger size. I haven't tried those... yet.
If he doesn't take to the e-cig at all, you might want to look into Snus for him. It seems to replace all we need from cigarettes and many vaping have switched over to it, leaving vaping and smoking behind. It is inexpensive and not messy. More information can be found in the Smokeless section of our forum:
Smokeless tobacco - E-Cigarette Forum
You get "good kid points" in my book for your Father's Day gift. Good for you! Let us know how he is doing?