who is she

Hi guys I recently got a 54 litre (14.2 gallons) aquarium from the Danish equivalent of Craigslist. It had this beautiful pleco in it and the lady said that she THINKS he (or she) is fully grown. He/she is about 9-10 cm (3.5 - 3.9 inches) As far as I know most plecos can get quite big.. Is...