Stephanie Seymour's Socialite Son -- Arrested for Living the High Life

Stephanie Seymour's socialite son may think about a move from NY to Colorado ... because then he wouldn't have gotten busted for weed.

Law enforcement sources tell TMZ ... 20-year-old Peter Brant Jr. was popped by cops in Red Hook, NY ... and charged with misdemeanor possession of weed. Cops wrote him a ticket and let him out.

The fine shouldn't pose much of a problem ... his dad's a billionaire businessman.

And his mom is a super affectionate ex-supermodel.