Christina Aguilera's son, Max, isn't a baby anymore!The singer's 12 year old boy made a rare appearance on his famous mum's Instagram this week and fans were blown away by how grown up he looked.MORE: Christina Aguilera reveals incredible new look and says she's done with dieting Christina posted a photo with Max, in which they’re sitting side-by-side playing a video game and not only were her followers impressed with her Mario Kart skills, they were thrilled to see a snapshot of Max. WATCH: