From Numbers 32:
11 ‘The men who came up out of Egypt from 20 years old and up will not see the land+ of which I have sworn to Abraham, Isaac, and Jacob,+ because they have not followed me wholeheartedly— 12 except Ca′leb+ the son of Je·phun′neh the Ken′iz·zite and Joshua+ the son of Nun, because they have followed Jehovah wholeheartedly.’+ 13 So Jehovah’s anger blazed against Israel and he made them wander about in the wilderness for 40 years,+ until all the generation that was doing evil in the eyes of Jehovah came to its end.
So Joshua and Caleb were the only ones part of the older generation (age 20+) to see the Promised Land. It took 40 years for that generation to pass away. It did not overlap with the younger generation who did inherit the Promised Land.