Depends on the items you are trying to gift.

If you are in Germany:

Valve recently "fixed" the issue that old games which received an age rating still could not be purchased.

However they forgot about the gift option, which is not visible for those titles.

I also noticed that the prices in the search bar and on the store page are different.
Clearly Valve messed something up.

I recommend posting in the "Bug Report" subforum with as much detail as possible.