Stick a photo of him and lots of stamps onto the envelope.

I heard that he retired

The way i heard it, his last big movie was going to be 'Chinese zodiac,' and now he's mostly retired.

Don't bother; he'll never even get a chance to see it.  Celebrities hire people or services to open and screen their mail.  Interesting offers go into a very small pile; most offers go into the round file (trash can).  All ideas go into the round file.  That's to protect the celebrity from claims, legitimate or not, of theft of intellectual property.  If the procedure is to toss all such mail, and the procedures are followed, the celebrity can defeat almost all IP claims.

If you have a real idea, you need to contact Jackie Chan's agent or management company and make an appointment.  Good luck with that!  Most will automatically deny you.  Two ways to get an appointment, or a restraining order against you:  persistence and creativity.  .

Reminds me of this:

http://www.reddit.com/r/todayilearned/comments/1u9bbw/til_bill_murray_does_not_have_an_agent_or_a/

The fact that Bill Murray doesn't have an agent, he just has a number that you call and pitch your ideas on his answering machine and he decides whether he wants to call you back or not..