I personally subscribe to the theory that Ship-Girls don't age naturally and only get "older" when they remodel or are relieved of duty. It helps let Destroyers enjoy drinking in-story if they want to, among other shenanigans.
Shipgirls have body that resists aging and is hard to kill Meaning she'll be forever lovely~
B-but she's an angel!
Here, I'm seven years old at my Shichi-Go-San.ceremony for 3-, 5-, and 7-year old childrenMy photo album. Brings back memories.How cute!And this was at my middle school entrance ceremony....okay?My journeyYou really look big-sister-ish.What're you looking at, Ryuujou-han?And this is at my coming-of-age ceremony.for those turning 20 years old...Do you not age, Ryuujou-han?