Unfortunately, we can't be precise. The film doesn't mention the ages of any of the characters, and the script, casting indications, and interviews are unhelpful. Also, the film has no novelization.
But we can reason that Chewie is in his mid-30s, in the following way:
- the characters are friends who all appear to be of a similar age
- the film is set in 2009
- the film starts with a flashback to 1980 where Jason witnesses his mother's death; Jason is probably less than 10 at this time
A time difference of 29 years added to Jason's initial age would make Chewie somewhere between 35 and 40.
None of them appears to be 40, however, so I'll settle on mid-30s.