Because of one special reason, I have to stay one certain GCC version. Are there any side effects? I 'm fine with a little performance degradation or larger code size, but I'm not sure if there are bugs caused by old GCC version. Is this possible to happen?
Yes, it's possible to happen... or you might have a bug with a new version of gcc.
That's the magic of software development... some bugs will have only been found and fixed in a later version than what you have... and some bugs will have only been introduced in a later version than what you have.
The general hope is that mature functionality will generally get less bugs over time. Whilst new functionality will have lots of bugs when first introduced, and will slowly get patched to reduce them.
If you indeed stick with an old version of GCC, eventually you will be left behind, and will not find new versions of the Linux kernel, or certain libraries that will compile under it (i.e. if you go back to before gcc pre-C99 you won't have fun times).
If you follow along with a relatively 'slow' moving OS baseline, like Debian. Then you're normally assured of a reasonably secure gcc release.