doesn't matter if the component is old it just that if your component don't have enough horsepower for the other one, it will bottleneck, when you buy cpu and gpu their price should be around $50-100 relative, like $150 cpu and $250gpu instead of $100 cpu with 300 gpu, but that's not alway the case, and depend on what will you spend on you can ask on forum like this , about the monitor it's not slow the gpu it just got limited like you using lower resolution monitor when your gpu could capable of doing higher resolution.
A bottleneck is a case where the performance of a system is limited by a components. These components that causes bottlenecking are mostly a cheap or old components used by a medium to high components. When you boost the frequency of that component, the bottleneck will be less, and therefore a faster system.
And you can say, yes monitor can bottleneck a GPU. But by the resolution. So when a monitor only support up to 720p, the GPU can't give out 1080p.
I would go a little more deep and expand the explanation.
In an application, depeding the workload, it always be a bottleneck.
Basically it's impossible to have a full equilibrated system, or the cpu, or the vga is more (percentually) requisited than the other.
Unless the software is very light in workload area, something you always bottleneck.. and still, the bottleneck shifts from one hardware to other based in the application and usage.
Basic quadcore + a nice GTX 560Ti
- Rendering an image without CUDA. CPU is limiting.
- Playing witcher 2, 1080p, maxed, ubersampling, 3d vision in 3 monitors.. hell yeah your GPU would be crying a lot..GPU is limiting