Hi synodontisjack,
my P.teugelsi also is about 20"+ (i had not took the measure since a longer time - maybe he's longer) ... i think the one you are seeing on the pic (from the member Loubard) is now kept by Guna (also member here - i do know him from a german board) and is also about 20"+ in lenght.
The information about the lenght of P.teugelsi which was made in polypterus.info was taken from the common publications about P.teugelsi ... up to this time P.teugelsi was really rare in aquaristics - i think the first description was made without having seen a real live specimen ... also with other mistakes - like black pectoral fins.
The reality seems to be quite diverse ... more and more people are keeping P.teugelsi, more exprerience is collected ... the best informations about P.teugelsi and all the other specimens of the Polypteridae i've read in American forums (THANKS ANNE!!!).
Greetings
Uwe