大約20、21歲開始，人類對夢境的記憶力就會開始衰退

大約20、21歲開始，人類對夢境的記憶力就會開始衰退

結果 (英文) 1:

From about 20 or 21 years old, human memory of dreams will begin to decline

結果 (英文) 2:

From about 20 or 21 years old, the memory of dreams begins to decline.

結果 (英文) 3:

From the age of 20 or 21, human memory for dreams begins to decline