I'm not sure about Android (as I've just been using it for few months), but my 2007 C2D Windows Vista is still running smooth (if you don't talk about gaming)

It doesn't really feel slower due to its growing age, but there are two possibilities why you think it's slower - and it probably applies to Android as well

- You install too much craps
- Your pc/phone can't cope with the latest apps as time goes because they are designed for more powerful hardware.