There's nothing to really man up about. It's "rookie of the year", it would be more weird to not consider age as a factor. A rookie who becomes a core go-to guy in his first ever year is just on another level than a Bunting and you seem to indirectly agree with your first sentence there. For me that's not anything controversial to state, so not sure why I'd have to "man up" about anything, like I'm making up an excuse for rookies like Seider.
I forgot to touch on your Panarin statement. Panarin deserved the calder at his age. He hit superstar status out the gate and ran with it since, so he's not a counter example in favor for Bunting. The whole hockey universe went on the edge of their seats for Panarin after his first few games. McDavid had no shot playing only 45 games and what Panarin did was more special than Eichel as well. Bunting isn't even close to Panarins rookie season in such a way he can offset Seiders age.