Summoned Items Can't Be Picked Up

When using the summon command to summon items, they can not be picked up.

I thought that when I summoned an item, it would appear on the ground and be able to be picked up.

The item did appear, but i was unable to pick it up. I did see a Zombie pick it up though.

The command I used was:
/summon Item ~ ~ ~ {Age:5400,Item:{id:skull}}