Do computers as time goes become laggy and slower?

 I'd just like to expand on it by a bit:

1) The hardware should operate at the same speed, but

2) Disk fragmentation takes a toll (De-frag HDDs on a regular basis)

3) Fatware (both as programs and the OS) is the killer. Every extra feature/security fix adds to the general overhead both in execution and in ultimate memory usage.

4) The internet & connectivity is also a killer. Your browser gets more & more overloaded with crud being downloaded with the web page you want to view. As an example, a simple newspaper article (without ad-blockers) downloaded 11 extra ads (3 of which were video ads)! So, in defense, use a Script killer & an Ad blocker.

5) Wear & tear. As the HDD ages, sectors go bad. While it's just a little thing to skip one bad sector, the cumulative effect can slow down your computer.

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To speed up your PC:

1) WEB Browser Script killers & AD blockers

2) Defrag your HDD

3) Defrag your Registry

4) Add extra memory, if not too expensive

5) Replace a 4+ year old HDD with a faster one, or an SSD

6) If a desktop, maybe get a faster CPU. Again, if you are daring & the cost isn't too great

7) The same goes for a faster GPU/Graphics card.

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I hope that this helps a bit.