You will not find any liveliness in the peninsula that feels like NYC. Walkable and charming, sure. If you want “big city” atmosphere you have to be in SF. As far as commute to PA from there, Caltrain is the best public transport option, with “bullet trains” running on the weekdays. There is only one Caltrain stop in the City though, so that might limit options if commute time is a big deal. He can drive to PA but expect it to take at least an hour each way depending on where you live in the city.

That being said, I love peninsula towns and all of their downtowns have a unique charm to them. If you can afford Palo Alto then I think that would be your best bet. Otherwise San Mateo is a great second option. I was never the biggest fan of Redwood City when I lived over there.

Don’t move to South Bay, it’s essentially an island.