Chances are if your Mac is old enough to attend kindergarten, it's not going to get the new OS X Mountain Lion.
But come on, isn't it about time you got a new one? In 2007, George W. Bush was in office and everyone was claiming the housing boom would go on forever -- perhaps you need to be just a little more modern.
TUAW made a list of the models that won't be supported. Read 'em and weep:
U.S. & World
- Late 2006 iMacs (iMac5.1, iMac5.2, iMac6.1)
- All plastic MacBooks that pre-date the aluminum unibody redesign (MacBook2.1, MacBook3.1, MacBook4.1)
- MacBook Pros released prior to June 2007 (MacBookPro2.1, MacBookPro2.2)
- The original MacBook Air (MacBookAir1.1)
- The Mid-2007 Mac mini (Macmini2.1)
- The original Mac Pro and its 8-core 2007 refresh (MacPro1.1, MacPro2.1)
- Late 2006 and Early 2008 Xserves (Xserve1.1, Xserve2.1)
This is a preliminary list, and as the Los Angeles Times points out, it could change and more Macs may get Mountain Lion than previously thought. (We have a feeling if there are a lot of complaints, there might be more machines receiving the upgrade.)
So what are you doing to do if you don't have that Mac? Well, it means you're stuck with OS X Lion -- which is probably decent enough since you have used it for the last six months. Apple said it will continue to support Lion for a few more years, but you must realize you will eventually have to get a new computer and enter the teens like the trooper you are.