We did a kind of this in real live this summer with two best friends of my wife. They were 19 and 20 years old, my wife is 26.
So they used a dildo we have here, which is 40 cm long...
So at the beginning they were only able to "plug-in" around 12-14 cm...
But after some more minutes and harder trieing the become deeper and deeper.. my wife at the end got 20 cm...
The oter one at the end was able to run 22 cm and the other one... 26 cm... and she is only 1.58 m tall......
We talked about this during the experiment etc and I'am still wondering where the 26 cm went into her....
Anyway,
next time we will do a video tape of this if we will try again and I will post it here... seems there are no other videos out there in the Internet...
Cheers
Thommy