Yes, great topic because I've also noticed questionable folks boarding early. This has in the past included a whole group of 5 adults with a single 12-ish year old child, only two of the adults I'm assuimg were the little ones parents and the others were friends/relatives travelling together.

It's one of those airport grey areas where the GA's have lots of discretion, whether they chose to use it or not. Most, in my experience, seem all too happy to avoid rocking the boat and let pax board uncontested.