I breastfed my daughter until she was three.
I breastfed my first until she was just over four, and only stopped because I was going through a very difficult pregnancy. My second is still b/f, mostly just at bedtime, and she's 38 months old.
There is no upper limit to breastfeeding, and studies have shown absolutely no harmful effects to so-called extended breastfeeding. As a matter of fact, children who are allowed to self-wean have been found to be more confident and self- reliant than those who are forced to stop.
You're doing the best for your child, and anyone who tries to tell you you're doing him harm is full of hot air. Ignore them.