The answer is man (or woman) At the start of their life, they crawl, on 4 limbs, At the middle of their life they walk on 2 legs, and at the end of their life they walk on 2 legs, but with a cane.
A human. Baby crawls on all fours Human walks on two legs in the middle of their life And 3 legs is when and elderly human uses the cane as a third leg