I don't necessarily have an age limit, but I've been gradually putting limits on my DD's nursing anyway. She's 3.3 now, but she's been slowly cutting back and I've been encouraging it. At this point we sometimes nurse 2x a day, sometimes less. I nightweaned her at over 2 and a half - so done with it at that point. As far as I'm concerned, if my body tells me it's time for a change, that's a sign I should listen to.
I feel like we're doing a slow, mutual weaning. I don't really believe in CLW, though, for myself - full disclosure. I was not comfortable letting DD decide alone as it's my body too and we are in a relationship. The weaning involved me gradually (like, over months) reducing the frequency of nursing during the day, and watching for signs of trauma. So far, so good. She's also had a couple of trips away from me. I see that psychologically, she doesn't NEED it the way she needed it at 2, so I'm comfortable with that. It's more just a love thing for her at this point, which is fine. But every kid is different.
If she's still nursing occasionally at 5, that would be okay with me. If she was nursing 3x or more a day at 5? Different story!