Re: Mid 50's father wants iPhone 6 plus or 6s plus
Hey, I'm a mid-50s guy who has been fairly ambidextrous when it comes to Android and iPhones - I've currently got the iPhone 64GB and I've not noticed any significant speed issues (even with iOS updates) on it.
Bear in mind that with iPhones, there is not the almost infinite number of variants that the Android OS has, so apps (and their developers) don't have to struggle as hard to make sure the app works as intended on the iPhone. By theory, that should make the apps less crash-prone and operate as efficiently as possible on the iPhone. And mostly, that's the case - certainly no worse than with Android.
The 'basics' as you describe should certainly not stress out the 6 at all. There are apps out there for the current OS that demand significantly more 'horsepower' from the OS and 6 than your father's needs. He may even find some of them over time.
Of course, with any piece of electronics, 'stuff happens' - hardware issue or customer accident may occur. iPhone comes with a one year hardware warranty (one year short of the upgrade date) - up to your father whether the AppleCare+ warranty expense is worth it. This would offer a second year of hardware, plus two instances of customer 'oops' care (say, dropping the phone and screen breaking), with a deductible that is cheaper than most of the repairs with Apple off-warranty. Given he's getting the phone for a $1 on this 2 year Plan, might be worth it? Or not. He could almost certainly get a cheap unlocked Android phone for about (or less than) the price of the Applecare + at, say, a Staples, if the unthinkable happens.
If anything, I'd recommend him getting a rigid case for the iPhone (yes, they really can bend - mine did a tiny bit before I got a chance to get it a case) and a screen protector, if the case doesn't include that. And battery drain was a bit surprising for me - big phone, more drain - and I wasn't prepared to hobble all the features that cause the drain (and make the phone convenient for me), so I sorted that out with a rigid case that included a battery pack (not Apple's and not Mophie - works just fine).
Two years should be just fine for your father. Heck, my backup if something goes wrong is an iPhone 4 which, up until 'upgrading' was still working just fine with all the apps I have on my current phone. And the 4 came out in 2010...