Transitioning to crib

My LO is 6 weeks old and sleeps next to us in a rock n play. He seems to like it, but he also seems to enjoy being able to stretch out when I have him napping in his crib during the day. What age did you all start putting your LO in their crib for the night? I know he'd probably be fine but I just worry about not being able to constantly check on him. Is he too young still?