If you want to store a date you don't need to store a time, time zone, etc. and your question goes away. Certainly if you want to store birth dates and do age

If you want to store a date you don't need to store a time, time zone, etc. and your question goes away. Certainly if you want to store birth dates and do age verification there is no point bothering with these issues, just store calendar date. Trivial to get date for age limit purposes.