In the Mirage Comics the Turtles were teens in the 80s. The series has had time skips and jumps (as most comics do) but the Turtles have aged based on that.
The Turtles count their age in years like humans do, and they seem to mature similarly to humans (though some might argue that different humans mature at different times). This may be psychological, though, as their psychology seems relatively consistant with that of a human as opposed to physiological.
There is no information as to their lifespan - even they themselves may not know until they start dropping dead from age-related illness (though, given that they are ninja, they most likely will not live that long). Warriors typically die by the sword, after all.