The 25-year-old set a number of new records in 2012, including the highest number of goals scored in a calendar year (91).
"How have I grown? Honestly? I have not evaluated it, I do not know," he told Argentine publication Ole. "I always hope to improve on everything. And that also includes my career, of course.
"I try not to think about my personal growth in sport. But obviously I am changing my mind as I get older, but I have not stopped to evaluate how things have changed in my game, at least, not yet."
Messi signed a new contract with Barcelona in December that will see him stay at Camp Nou until June 2018.