Does outdated CPU cause bottleneck ?

Yes it will bottleneck, if you think about Intel then to get most from gpu i3 at least is needed, and i5 would even make much better.
Use task manager and 'gpu-z' during playing games that you play, if your cpu usage is near 100%,a t least on one core, and graphic will be for example near 40% then your cpu is bottlenecking your gpu.
 
Generally speaking the more powerful the graphics card the larger the bottleneck will be for a Core 2 Duo CPU. However, the faster the C2D CPU, the lower the performance bottleneck.

The NVidia GTX 550 Ti is not a particularly powerful graphics card and you should not really have any bottlenecking issues with it. It's performance is between the Radeon HD 5770 and the Radeon HD 5830 back when it was released. Translated into more modern cards, it's performance would be between the Radeon HD 7750 and the HD 7770. The GTX 650 (vanilla version, not the Ti or TI Boost) is slightly more powerful than the GTX 550 Ti.

I currently have a C2Q Q9450 and a Radeon HD 5850 graphics card and I am not experiencing any bottleneck. Yes, it is a quad core CPU, but many games still only use 2 cores. For example, if I stuck the Radeon HD 5850 with a C2D CPU clocked at 3.0GHz, I should basically have the same performance when playing Skyrim since that game only uses 2 cores.
 
jaguarskx are you sure? ;] check you gpu usage during playing Skyrim.. I have pentium g620, and it's bottlenecking as crazy, 100% cpu usage, 30% gpu in many games (or maybe newer Radeons are so crazy..) beside that in other games your Quad Core is much faster than normal C2Duo..
One is obvious, better cpu will help to get more fps. There are some older benchmark so you can compare your cpu with other C2Duo to see difference, now they should be quit cheap - used models/ebay/auctions.
 
I'm pretty sure because when I play Skyrim @ 1920x1200 resolution with the HQ texture pack and some other enhanced high resolution textures, but no ENB, my frame rates are generally between 50 FPS to 60FPS. I only have a 60Hz monitor so 60 FPS is the limit for me.

My Q9450 is actually clocked at 2.8GHz (2.66GHz stock) 'cause I remember I was testing something in the BIOS and neglected to revert the settings back to what it was before; 3.0GHz. Also, the Radeon HD 5850 is running at stockspeed.