The action movie star shared the health update while celebrating his milestone 70th birthday on Sunday. Alongside a series of throwbacks, the action star reflected on his 6 decades in the movie industry, and confirmed he has no plans to retire.

He added ... "Not so long ago, a lot of friends saw some recent photos of me on the internet, and they were all concerned about my health. I want to take this opportunity to let everyone know, don’t worry! It’s just a character appearance for my latest movie. The character requires me to have white hair, white beard and look old."

JC said he felt lucky to be able to grow old, since many in the stunt profession don't always have this luxury. And, Jackie wasn't kidding when he said he was booked and busy ... as he has 8 projects in the works, according to his IMDB.

Jackie -- whose many credits include "The Karate Kid" reboot, the "Rush Hour" franchise and the "Kung Fu Panda" films -- received an outpouring of love from his famous friends and fans on social media.

Will Smith paid tribute to Jackie on his major milestone, sharing behind-the-scenes footage from his son Jaden's 'Karate Kid' film with the famed Hong Kong actor.

The Oscar winner wrote ... "I thank you most for helpin' to raise Jaden. Our time with you in Beijing during the Karate Kid left an eternal impact on our entire family. We wish you the deepest Love & Revelation on your next trip around the sun."