Its not absolutely mandatory to wait for six months period. You are actually required to produce content that is recognizable and considerably good in quality. If you have, let's say, 15-20 articles within six months period that have extremely good amount of regular traffic; you can consider applying before six months.
Another way to mention, I think getting AdSense approval through YouTube monetization is easy and you are not required to have videos/channel(s) that are six months old (I'm not sure though). If you get an approval through YouTube, you would need a domain of your own to get a fully approved AdSense account because the account obtained through YouTube cannot be used else where any more without up-gradation.