Numbers 14:33

ארבעים שנה [AND YOUR CHILDREN SHALL WANDER IN THE DESERT] FORTY YEARS — None of them was to die younger than 60 years old (Bava Batra 121b). For this reason a period of forty years was decreed for their wanderings in order that those who were at that time 20 years old (and only those from twenty years old and upwards came under this decree; cf. v. 29) should reach the age of sixty (the average age of man; cf. Moed Katan 28a and Tosefta Yoma 4:10. s. v. ומיתה). The first year that they were in the wilderness was included in the forty although it preceded the sending forth of the spies (which took place in the second year), because from the moment they made the Golden Calf this decree entered the mind of God, but He waited for them (postponed their punishment) until their measure of sin should be full. This is the meaning of what is stated, (Exodus 32:34) “And in the day when I shall visit — viz., at the incident of the spies — I shall visit their sin (that of the Golden Calf) upon them”. And, here, indeed, it states, (v. 34) “ye shall bear your iniquities” (in the plural) suggesting two sins; that of the Calf and that of the murmuring. — In the calculation it (Scripture) regards in the years of their lives a part of the year (of the sixtieth year) as the whole of it, and as soon as they entered their sixtieth year those who were now twenty years old died (Tanchuma 4:4:13). ונשאו את זנותיכם AND SHALL BEAR YOUR WHOREDOMS — Understand this as the Targum does: and they shall bear your guilt (cf. Targum on ונשא את עונה, Numbers 30:16, and Rashi on that verse).

וּ֠בְנֵיכֶ֠ם יִהְי֨וּ רֹעִ֤ים בַּמִּדְבָּר֙ אַרְבָּעִ֣ים שָׁנָ֔ה וְנָשְׂא֖וּ אֶת־זְנוּתֵיכֶ֑ם עַד־תֹּ֥ם פִּגְרֵיכֶ֖ם בַּמִּדְבָּֽר׃

And your children shall wander in the wilderness forty years, and bear your backslidings, until your carcasses be consumed in the wilderness.