It is very essential that you use a top-level domain name (e.g. .com, .org, .net etc).
It is noticed by the expert that if you use top level domain then your site is approved very fast by Google Adsense, even if you have only little posts.
Google always appreciate the top level and unique domain but if you write high quality and sufficient contents, for your blog,
then Google Adsense get approved without a top level domain.
Also when you have organic traffic then there is a chance that Google accepts your sub-level domain also.
In some countries like India/Pakistan, their domain should need to be 6 month old to apply for Google Adsense application,
but in some places this criterion is not fully obeyed by Adsense because some of the sites gain huge popularity in short time like my site https://talk49ja.com.ng,
so Google check if you have number of visitors,
also your posts, articles are unique so you will be approved fast.
As so many people are selling Adsense accounts through fraud methods,
therefore Google is now only approving accounts for people who have registered website more than 6-month-old.