301 redirect: does the new site get sandbox if I build backlinks quickly?

Hi everybody,
I have a more than 1 year old domain, now I want to buy new domain that includes the targeted keyword, and 301 redirect from old domain to new domain.
I would like to know if Google will consider my new domain as a new site or not? I mean, if I build the backlinks quickly, my new domain will get sandbox? Or my new domain will be considered as the replacement of the >1 year old site?
anyone had experience about this problem? please tell me!

Yes your new domain will be considered a new site. All the the 301 is going to do is pass the links on through to the new site from the old. It does not make your new site older or give it any special properties.

You need to login to google webmaster tools (create an account if needed) and on the left side there will be some categories, inside one of them is the option to "change your address". you can give google the new domain, 301 the old to the new, and verify that you own both and the majority of your SEO work wont be lost.

if you build links quickly to your new site then there are high chances of new domain getting sandboxed

The sandbox is more of a concept than a thing and only really applies to sites over a certain threshold. If you go for non competitive niches like local services, then you can get page one without sand-boxing. For areas like Viagra, mobile phones etc build too many links and you will be smited by the big G.