I would say that Ideally you would want him to beat a game that will compel him to play more games.
My mum (who's 55 years old) beat Uncharted 4 last year after my sister and I chipped in to get her a PS4. She was really blown away by the graphics and went on to play some of the prior Uncharted games too.
I think it's a good introduction, since it's got a fair set of accessibility features. It'll aim for you if you want it to, easy mode drastically lowers the difficulty, and so forth. My mum can't complete the tutorial in Plants Vs Zombies, but she beat Uncharted 4, and that really blew me away to be honest.
The only caveat I would say, is it sets very high expectations. After playing Uncharted 4, there's very few games that she's both interested in, are accessible, and feature similar quality. She could play something like TLOU, but zombies and horror aren't really her thing. Your Dad might be different, so he might move from Uncharted, to TLOU and games like Tomb Raider and Assassins Creed. All of those have great accessibility and that third person action style game is a genre that's well catered for so it gives them a selection of games to look forward to each year.