To combat credit card fraud, Valve has placed several restrictions on gifting.

Gifts can be sent to a friend, but not sold on the Market.
Gifts can only be sent to friends of at least one year, unless Mobile Authenticator is activated.
Items that were previously received as a gift cannot be wrapped again for one month.
Untradeable items obtained from drops or Treasures can only be gifted once.
Items from Treasures can be gifted again after their trade-restriction period expires.
Only a limited number of items can be gifted within a certain time. ( 8 items for every 24 hours )
The number of gifts one can send is determined by the player's Experience Trophy.
Non-tradeable items can only be gifted by players over level 5.

tfw I can finally vape

nintendogs