Kylie Jenner & Tyga -- Legally Cleared to ... Voulez-Vous Coucher in France

Kylie Jenner and Tyga still deny they're a couple -- smart since she's 17 and he's 24 -- but that's not stopping them from flying together all over Europe, where it just so happens the age of consent would be more favorable for them to ... y'know.

Tyga and Kylie were spotted together at England's Gatwick Airport on Friday ... then traveled on to Bordeaux, France and Geneva, Switzerland ... before landing in Athens, Greece where Tyga had a gig Sunday night.

Seems odd that Kylie would go on tour with Tyga -- if they're just friends -- but then we noticed the age of consent for sex in those countries:

England -- 16
France -- 15
Switzerland -- 16
Greece -- 15

The consent age is 18 under Federal and California law. Of course, there's still no evidence they're banging -- and Tyga's been adamant they're NOT -- but ya gotta wonder if they read up on international laws before departing ... just in case.