Data was designed to age. From the TNG episode
"Inheritance" :
LAFORGE: Basically she's a
Soong-type android, except everything about her is designed to fool you into thinking she's human.
CRUSHER: She's got tear ducts, sweat glands, even veins and capillaries underneath her skin.
RIKER: Why does the scanner read her as a human?
CRUSHER: Because she has a feedback processor designed to send out a false bio-signal.
LAFORGE: It's part of her aging programme.
Not only does she age in appearance like Data, her vital signs change too.