俱舍論記 11.110

11.110

「人五十歲至萬六千歲」者，答。欲界六天已上五天，望下四天王天各有二俱增倍：一晝夜增倍、二壽量增倍，故言上五欲天漸俱增倍。餘文可知。

Regarding "Fifty human years […] sixteen thousand years": this is the answer. For the five heavens above the six heavens of the desire realm, in comparison with the Cāturmahārājakāyika heaven below, both [aspects] double for each: first, day and night double; second, the lifespan doubles. Thus it is said that the upper five desire heavens gradually double in both respects. The remaining text can be understood.