Tom Hanks was born on July 9, 1956, so in the film Big (1988) he was about 31 or 32 years old, depending on the exact filming dates versus his birthday. Specifically, since Big was released in 1988, Hanks would have turned 32 that year. If you’re asking about his age at the time of filming, production on Big occurred in 1987, so he would have been 31 at the start of filming and turning 32 during that year.