How long was the in-universe span of the show?

[sdp]

In the 2k3 forum we're discussing how long the turtles were "active" here and I wanted to have the same discussion for the OT.

Basically how many years happened between the first episode and the last. Do we know how old the turtles are?, I'd like it if the ten seasons happened and the turtles could still be teenagers, I'm guessing that might not be much of a problem. I think the entire show could have happened over the span of 4/5 years? Thats plausible it could have happened even before.

The main problem is the shows "present time" in the first season would technically be 88 or 87 (the turtles are called 88 in Turtles Forever). The technology/fashion/etc all reek of the late 80s, however the last few seasons are clearly taking place in the mid 90s. I guess the show could start in the very early 90s since those early years was still transitioning from that stench of the 80s (:p) and that way the timeline could work better but i don't like messing with the fact that they technically started in 88.