I walked to the right (J) side of the lounge entrance and presented my boarding pass to the agent there? Is there another way to do it in BNE? Celebrity - probably not, they could tell by the name on the boarding pass anyway. Security - maybe, but if it's just based on my description, an ID wouldn't prove that they weren't looking for me. Looking jet-lagged is possible given the transit from the international red-eye.
I haven't looked young enough to be requested for ID the other 80+ times I've walked into airline lounges in the last year or so. Or even when requesting alcohol at the bar.
Seems like this was a once-off occurrence, given no one else as experienced it. I'll put it down to looking not so great after my international long haul I suppose.