Tips on buying a BMX?

I'm 13 and looking to buy my first BMX. My mates have suggested getting a Mongoose off the internet, but on the ones I'm looking at it says 'boys' as the gender/age - is that okay or is it a little kiddies bike?http://cgi.ebay.co.uk/MONGOOSE-SUBJECT-2011-BMX-FREESTYLE-BIKE-CHEAPEST-NEW-/400206219703?pt=UK_Bikes_GL&hash=item5d2e2649b7#ht_5398wt_1139 < That's one I'm thinking of, would that be okay for me and has anyone got any other tips for me?