Aging in the NBA is an interesting thing.
On the one hand, you could say that Butler's game never relied on great athleticism so he should age well.
On the other hand, what we see a lot is that guys who aren't particularly athletic can't afford to lose any of that athleticism.
This comparison is a little oblique but I think about how much more skilled as a basketball player Pierce was than Vince Carter but Carter's career lasted longer because he had athleticism to spare. Pierce, although more skilled in ways that didn't necessitate athleticism, didn't have that.
Butler is a smart player and a hard worker but he drastically changes his game, it's hard for me to imagine him being productive for much longer and certainly not in any other context than the Miami Heat.