DD1 lost her latch at 3.6y/o - which is early but the space for the first set of adult molars had appeared and that changed the shape of her mouth/oral cavity making it impossible for her to latch.
She was causing pain for about 2 weeks with sloppy latching (messing about with her tongue/teeth/on & off) before she just couldn't latch at all. I had originally put it down to being 8m pg but DD2 wasn't hurting me just DD1.
It was actually quite funny to see her try to latch that last time - she'd stick her tongue out and 'gurn' in an attempt to get her mouth/tongue in the right place to feed but she just couldn't find the sweet spot so to speak. I am a mean mummy though 
DH and I explained what had happened and that she was a really big girl now and made a big fuss of how grown up she was. Then DH cried because DD1 didn't have any baby left.
That's not saying bfing is just for babies but that she had potty trained, wasn't fed from a spoon, didn't need rocking and now didn't bf - it was the last of the baby she once was, was gone.
She now has 2 of the adult molars (got them sometime before Xmas) and 2 are erupting now and she is 4.11y/o.
Can you check to see if your DS has more space at the back of his molars/extra gum space on the jaw as if that is the case he might be on the last leg of his bfing journey.
I probably should ask how old he is but I think I recall he's about 5? Or am I mixing you up with someone else?