6 month domain age means very little now days. For low competition phrases ( obviously depending on the phrase and perception of "low competition" ) Its possible to get first page positions within days/weeks and first place a reasonable amount of time after with the right content and strategy.
If its a localised phrase as well then it could be even quicker.
What kind of content is on the page/site in question ? Would be interesting to see more details about this particular case so we can make a reasonable judgement