John Gill Commentary Joshua 13:1

"Now Joshua was old and well stricken in years; and Jehovah said unto him, Thou art old and well stricken in years, and there remaineth yet very much land to be possessed." — Joshua 13:1 (ASV)

Now Joshua was old, [and] stricken in years
How old he was cannot be said precisely, but it is very probable he was now about an hundred years of age, for he lived to be an hundred ten; and the land of Canaan was seven years in dividing, as the Jews generally say, and it seems as if he did not live long after that:

and the Lord said unto him :
either spoke to him out of the tabernacle, or appeared to him in a dream or vision:

you are old, [and] stricken in years, and there remaineth yet very
much land to be possessed :
that is, very much of the land of Canaan, which God had promised to Abraham, yet remained unconquered by Joshua, and unpossessed by the children of Israel; and the old age of Joshua is observed, to intimate to him that through it, and the infirmities of it, he was unable to go out to war, and to finish this work, which must be left to be done by others hereafter; and that he should with all expedition set about another work he was capable of doing, before he died, which was the division of the land among the tribes of Israel.