Could Elsa's birthday be on summer?

I know, I know, it sounds silly, but Elsa is crowned queen during the summer season.

Elsa can only be queen once she was 21.

So... does that mean that Elsa's birthday could have happened recently? 'Cause Arendelle needed a queen (or ruler) right away, since they haven't had one for three years, so most probably her coronation was exactly her birthday, or a few days ago.

She may be also born of winter air (like the song) but I don't know...

What do you think?