Aoki Lee Simmons, 21, was spotted on a romantic getaway to St. Barts with her much older boyfriend, restauranteur Vittorio Assaf, 65, RadarOnline.com has learned. Aoki — the youngest daughter of Kimora Lee Simmons and music mogul Russell Simmons — and Assaf returned to the island where their May-December romance began. On Tuesday, Aoki and Assaf were seen soaking up the sun during their romantic vacation. Aoki, who graduated from Harvard at age 20, was spotted planting a kiss on the Serafina Restaurant Group founder. In between their PDA moments, Assaf was seen taking snaps of Aoki posing in a…