He's almsot 2.5 and we still have mesh / breathable bumpers on. It keeps his arms and legs in when he sleeps. No intentions to remove them until he's out of the crib.
We just went to a bed but had the mesh bumpers on until then, he is 2.75 yrs old. I would only take them off if they are using them to try to climb out.
We took them off around 14 or 15 months when she puked all over them early in the night. She made it through the rest of the night fine, we didn't get around to putting them back on the next night, and decided just to see how it went. She's 18 months now and hasn't cared; I think she knows how to get her limbs back in so it doesn't wake her up like it used to.