Yes my Mac is 4 years old and upgrades just fine to the latest Yosemite OS.
Same here but I've upgraded the memory to 8gb of ram and changed the hard drive to a 500gb SSD drive. I suppose the battery will be the next change but for now it's fine. I back up once a month and remove stuff that's not used. Whilst my iPhone and iPad do much of my work my Macbook Pro is king!