[Grammar] since when did/has

[Fagin]

Is there anything wrong with any of these questions?

Since when did it become cool to be shy?
Since when has it become cool to be shy?
Since when did being shy become cool?
Since when has being shy become cool?

And which is the most natural way to say this?

 

[J&K Tutoring]

All are okay, but I think maybe it would be more typical to hear, 'Since when is it cool to be shy?'

Not a teenager.

 

[emsr2d2]

If I had to choose between your original four, I would use 1 and 3 (had you numbered them).