What a dumb idea. Seriously dumb, not to mention insulting to your target market.
Being a senior citizen doesn't mean you suddenly become dumb as a brick, what it is likely to mean is impared eye-sight and/or hearing.
The main problem with mobile phones (and this from the experience of my 87yo Father) is that the buttons and screen text are too small. All that's needed is a phone with large buttons (so it can be clearly seen which button is being pressed), the numbers on the screen nice and large and a decent speaker so someone with less than perfect hearing can understand the person on the other end.
As to knowing which number to dial? On his land-line speed dial has been setup for each of his regular contacts with an insert listing them. Absolutely no reason why this couldn't also be done on a mobile phone.
He doesn't need all the stuff your average smart phone does, so a simplified user interface with the emphasis being on making phone calls (which most people seem to forget is what the damn thing is for anyway).
Some things do not need a complex solution. Keep It Simple, Stupid.