Welcome to PT tatedart.

My Mooky use to suckle also when he was young, but he outgrew it.
My sons cat Sades is just over 2 years old and still suckles on our necks. It is comforting to them. I find it endearing.

They say it is because they were taken off their mothers too young. If it bothers you that your kitten does this, please don't push him off of you, just pick him up, put him gently on the floor and walk away, or distract him by playing with him. Gradually, he will get the hint.