i heard that if the keywords are matching exactly with the domain name then it should come first.
That was very often the case a while ago - just the exact match of the domain name helped a LOT. But last September Google took some steps to remove any ranking advantage that came from the domain name. We called it the EMD Update (for Exact Match Domain), and you can read more about it here: [webmasterworld.com...] and here: [webmasterworld.com...]
My domain age it more than 5 months and more than 400 posts.
You will probably need real links from other reputable sites to improve your rankings.
You will also need to check for other EMDs using the same four keywords in a different order, these may be competing for authority for the four words but only Google knows for sure.
Scrapers, feed repeaters and the like are also to be checked out as they often automatically re-publish content on a per keyword basis and you might be triggering several of them.
example: Google the very title of this post and you will see it posted verbatim on another site already, automatically. While this post outranks that post they are still 1 and 2. That effect is more intense with more competitive keywords.