it has a great effect on the sites being index so how can they be rank compared to the old sites? which will be prioritized the new one or the old one? how are they ranked with this sandbox?
Sandbox is a "theory" by my opinion, it was never claimed from someone from Google that it really exists. If you have a new site you can monitor it's moving up and then it can happen it won't continue to move up regardless of SEO actions you do. This period can last from 3-9 months (by pobservations of some webmasters on forums). Old site (1 year+) is supposed not to be affected by sandbox. You can avoid Sandbox with developing a site offline and launching it when there is all set up (design, links, major content). After launching you continuously update it and care about getting backlinks on a regular basis.