I have a 3 year old 15" 2.4 GHz Intel Core 2 Duo MPB that I upgraded to 4GB of RAM about a year ago.
Before I made the switch to Apple I used to feel the need to upgrade my Windows based laptops every 3 years, that's about when they started to feel sluggish. After paying double what I would pay for a Windows machine, I'd hoped I might be able to squeeze a bit more life out of my Mac, maybe 4 years. But it's coming up to its 3rd birthday and it's starting to feel a little sluggish at times. In fairness, it is mainly when using apps like iPhone 11 and Final Cut Pro X.
I replaced the 250GB drive in it with a 500GB 7200RPM hard drive about 18 months ago, so I sometimes wonder if that could have introduced a problem that might be causing it to run slow.
So my question is: is there a way to test the HD, RAM or other things to see if there's a problem with my setup that could be easily fixed, or am I just expecting to much of my machine?