I know parents who moved their babies into their own room at 4 months, but they were sleeping through the night and outgrowing their next to me cots. I co-slept with my baby until he was 5 months, and then he went into his own room purely because we were disturbing each other and I was waking up and comfort feeding every 45 minutes. It was honestly a desperation thing, and it broke my heart to do it. It worked for us, just to get the first long stint of sleep in, and then more often then not he'd come back into our bed. Only now at 7 months is he in his own room properly (and to be honest, still ends up back in our bed in the morning!).
You absolutely have to do what's best for you, but the guidelines are there for a reason and with such a big online presence, he shouldn't be bragging about moving little Marley into his own room so early. If he wants to do it, that's up to him, but there's no need to document it and influence thousands of others to do the same. Given Marley's history, I wouldn't be carting him off to his own room this early.