How many years will my Nikon d5000 last?

I read somewhere that the amount of shots also matters. Maybe about 100, 000 shots. Why does it matter how many shots are taken? I take VERY good care of my camera. I've had it for nearly 3 years.

The 100, 000 actuations is what the shutter is rated to. This means that when Nikon tested the camera they found that some of the shutters started to fail around 100, 000 shots.
Your camera will last you as long as you need once you take good care of it. If the shutter fails (which can happen to anyone, regardless of how well you take care of your camera) then you can easily get it fixed by Nikon.
I've been shooting sports professionally for many years, My Canon 1D Mark IV was rated to something like 300, 000 actuations when I got it. I had to get the shutter replaced because it broke after 500, 000 actuations and I take exceptionally good care of my cameras. My other cameras have never had the shutter fail on me and I've had some of them for longer.

I would say another 3 years at least. 100, 000 shutter cycles on such a new camera tells me that you might be over shooting a little.
If you get into the habit of composing your shots and then getting a great shot each time you press the shutter release, your shutter cycle count should drop quite a bit.
I have an old Nikon D100 that has just over 220, 000 shutter cycles on it and it was purchased in 2002.
Basically you can use your camera until the shutter stops working and you start getting half images when you take a shot.
I have a colleague that has over 1, 000, 000 shots on his Nikon D3 and it is still working just fine.
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