I love hearing about all these old plecos! I wonder which of us will be the first to hit 20+ years old with a pleco? 

I wasnt saying that is how to tell the age. Just stating the irony. I would say he is full grown and have not noticed any new growth the last few yearsPerhaps, but fish generally grow faster when they are young and slow down a lot with age. So 5 years ago it was perhaps an inch or two shorter, not 5 inches.