That doesn't sound like the words of someone who thought he aged like a normal human.
No one ever said he aged like a normal humn. Just because his appearance changes subtly over time, doesn't mean he will look a human 900 when he gets to 900. And who knows, he may be able to reset the program to 'start from scratch' if he wants.
Huh. I don't remember Data being referred to in that line.
Nevertheless, it's there. You can check if you don't believe me...I won't be offended.