Many airlines make it a point to invite premium passengers to board last, particularly if the lounge is close to the gate so there are few timing issues involved.

My favourite example is the BA lounge at MIA, which is just upstairs from the gates that BA normally uses. There is no PA system, so the lounge agent has to come in and make a personal speech. The usual agent does two: One when boarding is just starting, in case anyone really wants to get on board first. But she advises everyone to wait comfortably in the lounge until boarding has almost finished. At that time, she comes back and makes a second speech, saying that it's time to go. And it is - by the time everyone has got downstairs and onto the aircraft, they're ready to shut the doors and depart. The lounge is a much better place the aircraft seat for those last 30 minutes of waiting.