How long to ferment?

On Sunday 6/9 I brewed my first batch of beer (Sierra Nevada clone). From what I have read it only needs to ferment for 1 week but the guy who lives next door who has been brewing for a while suggested that I ferment for at least 2 weeks.
Is this just a personal preference thing? Is it better to ferment longer?
Thanks for your help.

Thanks for your help

Some ferment up to 8 weeks. That beer wouldn't hurt to sit in primary for 3-4 weeks. The yeast does a lot of cleaning up in that time and the taste will drastically improve. Unless you're moving to secondary for dry hopping, one week is simply too short.

+1 to above

Thanks for the input... I decided I will let it ferment for at least 2 weeks

I may be a bit of a noob, but I tend to follow the 2/2/2 rule. 2 weeks in the primary, two weeks in the bottles to carb up (probably longer than it really needs), and then two weeks of conditioning to drink.

Note, I'm also not worried about clarity or any of the appearance factors, only if it tastes decent.

I am Drinking an IPA that is exactly 17 days old that I bottle conditioned 4 days primary it dropped clear then 10 days in bottles and I drank the first one on friday 14 brewed on Saturday the 1st. Friday the beer was noticeably green yesterday (17) it was great. It was a low gravity IPA 1.050 and was completely cleared in my conical on the morning of the fifth day so a bottled.

It can be done, but patience is usually a virtue for most styles of beer. The key to a quick turnaround are SG and pitching enough healthy yeast IMHO and Temperature. This beer fermented at an ambient 62F with s-05 the conical was about 5 degrees warmer.

For A new brewer I think the 2-2-2 rule is a pretty good one to follow because you just probably don't have your process completely down yet and have no experience with the recipe or the yeast strain that you are using. After a couple batches you will start to know when it is down by the way it looks and the hydrometer and then if you choose to you can speed up the process as much as nature will allow.

For my ipa/dipas I'll go 2 weeks at 65-68, cold crash for a day or two, raise back to 65, and then dry hop for 5 days with 3-4 oz of hops. Keg at the three week mark and am drinking by week 4.

For malt forward, higher gravity beers that use a lot of specialty malts I go a month in primary, and then keg and carb. Drinks well by week 6.

I have found that if you control fermentation temps, and pitch the proper amount of yeast you won't have to worry about "green beer".