Shouldn't all of group 16 form double bonds?
I notice that out of all of group 16 oxygen is the only element that can form a double bond.


This premise is not true. Sulfur in fact forms double bonds in many organic compounds.  Selenium and tellurium both form double bonds with triphenylphosphine as triphenylphosphineselenide and triphenylphosphinetelluride.

The larger chalcogenides do have difficulty in forming double bonds in organic molecules due to lower bond strength, higher reactivity, preference of molecules for oxygen, and steric bulk.  They can however indeed form double bonds; it's just not as common.