Actually, Spider-Man was the lead character in "Life story", but it applied to all the universe. Captain America, Iron Man, Reed Richards, they all aged as well.
Besides, the effect could be noticed because that story covered several decades in a short real-life publication time. A universe being published and advanced in real time would require decades for this effect to be noticeable as well, and even then people may not notice it. Ultimate Marvel was the longest of that kind, 15 years, but not even that would be enough: the world of 2015 is not all that different from the 2000 one. If Franklin Richards was born in a FF #1 that started it all, by that time he would still be a teenager.