OK, I voted not retractible.
However, in the early half of age 2, DS did retract himself a few times and was half fascinated and half scared, I think. (mostly fascinated...
He even asked me to help him retract a couple of times to see the glans, but I told him that that was for him to do. Then once, he got a little stuck and that scared him. He asked for my help to get the foreskin back over the glans and I certainly helped then!
He plays constantly, but there has been no more retracting to my knowledge for about 9ish months... It seems to still be adhered again, but I don't really check enough to know.