Usain Bolt -- I'LL RACE 105-YEAR-OLD ... Let's Do This!!!

Usain Bolt says he's NOT AFRAID of a challenge ... even if it's from a 105-year-old man ... telling TMZ Sports he's absolutely down to race the centenarian sprinter who called him out!

The challenger is Hidekichi Miyazaki -- aka "Golden Bolt" -- who set the world record in the 100 meter dash for people 105-years-old and up with a time of 42 seconds.

After the race, Miyazaki did Usain's famous lightning bolt celebration -- and challenged the Jamaican to a race!

Now, Bolt's agent Ricky Simms tells us, "Usain would be delighted to accept the challenge and meet Mr. Miyazaki the next time he is in Japan."

Miyazaki better start training ... Bolt's last 100m time was 9.79.

Good luck!!!