They make it pretty clear Bolas is feeling his age in Shards. But they seem to have heavily implied in recent stories that after the Conflux Bolas got enough magic power to stem back his aging. I haven't read the Shards book in a while, but if I remember right the part where it talks about Bolas aging is from his perspective. And we all know he has a flair for the dramatic.
But they have also been very hit an miss on the effects of aging after the mending.
I might be a bit late, but for what it's worth, here's a quote fom the showdown of
Alara Unboken, when Bolas has absorbed most of the Maelstrom and is stepping out of it again:
It was unmistakably Bolas, but Ajani thought he looked larger than he had been, or somehow more grandiose. He had no scars or wounds, no frayed scales on his pinions, no scruffy patches at his joints. He was smooth, sleek, a study in armored scale stretched over lean muscle. (p. 352)
So, yup, it's made quite explicit that he looks younger and fitter than before (especially if you compare it to his description on the first page), and Ajani can see it too.