Hi my friend,
"There are watches for young people, in the PP family. Come to
mind models like the Aquanaut, the Nautilus ( the Chrono being, in my
opinion the one which looks the younger model ), the 5070 ( especially
the P ), and even the 5140 P."
I don't agree. And none of them is a simple Calatrava which is my subject! 
"About Calatravas, which is your main interrogation point, maybe PP can play on the color rather than on the style of the watch?"
Maybe?
"Let's
imagine a blue dialed Calatrava, for example. If it works for the 5140P
( which amazingly has waken my interest up for the 5140 ), why not for a
Calatrava?
White metal, blue dial...That would be cool."
Sure, but that can be very old fashioned too, so it needs a daring design.
"I
don't believe in some watches like the VC Quai de L'Ile or the RM 5 /
10 fro a brand like PP, it would be too weird looking, in my opinion, as
it is obviously not PP's Credo."
Neither do I, but they need to find their way!
"But playing on the color of the dial may do it!"
Yes but that would not be enough IMO.
Cheers
Dje