Separation anxiety

My son is I only 9 weeks old and seems to suffer from separation anxiety already. I was just moving and had to leave him with my brother and sister in law and he apparently cried for 30 min before he finally cried himself to sleep. Is this possible since they say it usually doesn’t occur till they are around 6 months or older?! And how do I help him get adjusted to not having me around all the time, especially when I start back at work and he’s left with other caregivers??