Time duration between first time domain registration date to today is called domain age.
Just open any domain checker tool
Submit your website and see website age.
Check here example:
If my domain is very old that mean my content quality will be good?
No! This is not necessary.
Domain age is not an indication of good content quality.
There is a policy in few countries that they do not public domain age. And many people make their domain registration date private. How will Google figure out age for them? There is no way to get this.
Does old domain represent trust, reputation and big brand score?
That is why Google give benefit in overall Ranking, that is true?
Many people buy old domain and try to get this benefit but Google aware with this trick and I don’t think Google will pick domain age for website reputation and trust.
Google also have given reply on twitter about Domain age, see Google’s statements on domain age and domain registration length.