Gambit is a total Scorpio.
Scorpios are very secretive (like him), they bury their past and transgressions deep within (like he does), Scorpios make exceptional and skilled fighters, and are known for their intense, and charming eyes (who else is known for their unique eyes?). Even the fact his eyes are red and black, is very Scorpion in nature.
Also, Scorpio controls sex, and Gambit is the most sexual of the bunch. They are also associated with "The Occult", kinda like Gambit's association with the Guild, and their mysticism. Despite being a water sign, Scorpios are known to possess an intense fiery energy within, which is where they draw strength (like how he draws kinetic energy). The only trait Gambit doesn't have much of, is being emotional. However, that can easily be explained by his rising sign, which is either Aquarius or Aries, based on his rebellious, fiery and cocky nature.