The 31-year-old returned to Italy after seeing his career stall following the move to Real Madrid in 2009.
The attacking midfielder is hoping to rediscover the form that saw him score 95 goals in 270 appearances in his first stint at Milan, with his first aim being to get to the 100-goal mark.
"I only lack a few more goals before I reach the 100-goal achievement with AC Milan. I only need five more," Kaka told Radio Jovern Pan.
"Hopefully I can get to that achievement this time. If there was a chance I could play with Brazil, I would not have any problems."
Kaka signed a two-year deal with Milan and will wear the number 22 shirt.