It was suppose to be current age but it can be either, that probably makes for a better topic.
At his current age they only one that makes sense to me would be Mayweather since he'd still be competitive.
In their prime however the one guy I'd bring back is Mike Tyson. The dude would wreck this HW division, and in his prime the guy was must see TV. There was no better buzz around boxing than when Tyson was fighting.
Like come back at his current age or come back in their prime?
It was suppose to be current age but it can be either, that probably makes for a better topic.
I'd probably pick Mayweather because he's the one in recent mind that I'm sure could still fight.
Selfishly, however, I might pick Sven Ottke, because I hated him and wanted to see him lose.