I know for India publishers websites have to be 6 months old or older.
For USA publishers you can get your website approved with a 1 day old website.
But it's better to wait anyway to get your website going and start writing content and then over that time get traffic going to it.
Traffic isn't required for getting approved, but without website traffic nobody will click on your ads and you won't make money anyway.
It's better to get traffic to the website and then apply and use adsense.
No point in having an approved adsense account if you aren't making money.
And to make that money you need traffic and you needs lots of traffic such as 4,000 daily visitors to make any money with adsense.