its a new social network, and the SEO person says he can do that.

As long as your SEO person is:

1) conducting a serious competitive analysis on your competition
2) is targeting the right keywords
2.1) casting a wide net with low hanging fruit keywords
3) ensuring your site structure is sound
4) you are using effective url structures and not some scripted output gibberish urls like$%%
5) ensuring your site is active in publishing new information with text and other media formats that is easily crawlable
6) Acquiring quality backinks, one way backlinks and use of a good anchor text strategy

…yes it can be done.

An aged domain that has some backlink history can help quite a bit dependent on the competitiveness of your core keyword phrase(s) you’re going after. New sites occasionally have difficulty, way ranking #1 organically for the term ‘mortgage’ if you know what I mean.

Hope this helps.