Mine is about 25" & 3 years old. She smacks the glass all the time, attacking fish in another tank across the room. The worst thing to ever happen was a split lip once. I look as it in a positive way-she chips her teeth so I never need to worry about them getting too long. The last thing I ever want to do is trim her teeth. She is the funnest fish I have owned in the 45 years I have been in the hobby.