That's true, but it should still be very obvious. No teenager has a voice that deep. Just because it's anime, doesn't mean you can't tell what age they are. I usually guess what characters age they are in anime, and I get it right almost all the time. Also, just take a look at his body and how tall he is. (Though, I have seen taller characters than him.)
The voice and looks usually define a characters age.
Also, I really like the art style in the 2004 series cause it reflects Dr. Tezuka's artstyle. (I think retro anime styles look cute.

)
You are probably thinking he mostly has a feminine look sometimes, which could lead you to thinking that he may be in his teens. Though as for me, I already knew he was somewhere in his thirties just by taking a close look at him, paying attention to his background story, and listening to his adult voice. (I have noticed that he sometimes looks like a female in some frames, But that's usually the type of expressions he has on his face.)

EDIT: Something else I forgot to add. Tezuka usually creates all his characters with certain looks and detail that other anime or manga characters don't. So, in his works, there is no need for any age. You can usually tell what age they are in his works just by looking at them. (That's one of the small reasons why I like his works.

) But as for one of those characters with a background story, like Pinoko pretty much, it's kinda hard to tell, but can usually be revealed by just paying attention to her actions and personality.

Trust me, I'm an Otaku. I know these thing very well, for I have been around anime and manga ever since I was like 5.
