Generally no, you cannot install an older OSX version than what it shipped/came with.

What Konix said.

You can use Scratch Live and Serato DJ with Yosemite.

Do you guys think a 2012 macbook pro would be ok in terms of CPU meter in serato dj not having much usage?

Macbookpro mid 2012 2.7ghz i7 16gb ram and dont even use 10% CPU with every serato add on you can get. Oh and Yosemite 10.10.04

Any ideas where i can get a 2012. Looked everywhere but no luck with those specs

That's the last of the bigger body style too, non-retina so like the 2011 17" models they are a premium to a lot of DJs. Ebay is probably your best bet along with trolling craigslist now that they are a 3+ years old.

If you want SUPER reliable reseller that will cover you if something breaks on an older models (but you might not get the -cheapest- deal) OWC is good.

eshop.macsales.com

On that note... damn!

eshop.macsales.com

$900 with the dedicated video card too, good starting point for someone getting into VJ'ing. That's the same model I have and it plays everything up to 1080p in SDJ/ME with no problems.

Thanks guys... If any other place to see a mid 2012 mbp please post a link ... Thanks

I have an early 2009 17" mbp and have upgrade the RAM and installed a SSD... But i guess my processor is the one who make serato dj use 30 to 40% of CPU so i see the green bar go up to that much

Just an FYI, Apple still sell this model, it's the last remaining CD drive model they sell.
(last update was Jun 2012 so it's the same as the 2012 models you guys are talking about)

I would just buy it new with warrantee if I was you.
store.apple.com

Nope we was on a out the 15" model