"If you think that's a benefit," Emerald Sparrow said ambiguously.
For the sake of eternal youth, those who choose to join the Kingdom and continue to be Magical Girls after their ten years of service are not few in number. Although their lifespan does not increase, the bodies and true forms of these Magical Girls stay young in appearance until the end of their natural lives.
This has always been the excuse used by Emerald Sparrow to explain to her juniors why there is almost no difference in her appearance before and after transformation. Thankfully, this excuse holds up, as Asou Haruka, who recently moved to Fangting City, also used her appearance to corroborate Emerald Sparrow's story, and nobody could poke holes in her identity through this excuse.
"Of course, it is a benefit."