Arnold Schwarzenegger's no longer just wining and dining new GF Heather Milligan ... he's showing her off to friends during double-dates.
Arnie and Heather hit Spago in Bev Hills this week with another couple ... we're told the the guy is an old friend of Arnold's.
By the way, Heather is reportedly 38 years old ... while Arnie is 65 -- and his buddy seems to be around that same age.
Sooo ... gotta wonder what the dinner conversation was like during the foursome's night on the town.
FYI -- When Arnold won his first 5 Mr. Olympia titles, Heather hadn't even been born yet ... when he starred in "Conan," she was 7 ... and when Arnold secretly impregnated his maid while still married to Maria Shriver, she was only 23.