Not to discourage you, 40 is a bit too old for an mba. maybe an EMBA suits your need better. But if you look at the age range for top programs, there are actually some close-to-40-year-old admit(s) .
The oldest mba i ve met in person was 35 when he enrolled. You can just give it a shot, who knows what the outcome will be. wish you the best of luck.
It all depends on what you want. If your plan is to come back to China and work in a friend's company, you really don't have to get an MBA from a top school, or even a school in US.