Is my 20+yr. old sucker dying?

Question
my sucker fish that i have had for more than 20 years is laying on its side on the bottom of a 50 gal. tank.  i dont know if its sick or just old. its never been sick so i dont really know what to look for.  its eyes and fins look norma its breathing normal and the oscar that shares the tank seems healthy.  how long do they usually live and is there anything other than the normal(ick, etc.) i should be looking for?

Answer
Hi,
I think the life expectancy for:
large pleco= 12-18 years
small pleco= 4-12 years
twig catfish=4-8 years
armored catfish= 18-30 years
cory= 2-3 years
other= average is about 10 years, but I have heard fish stories about fish in the wild outliving people.

Make sure the D.O. is high enough, that's normally the problem with catfish.