I'd say its a dominance thing. The older ones are establishing territory and that they are boss, as said above. However, be very careful keeping very many hamsters together. I used to breed dwarf hamsters and even though they were supplied with plenty of food and water and babies were handled from about a week old, when I put more than probably two together they started attacking each other viciously. They were ok at first, then they randomly started attacking as the babies got bigger (all seperated males from females). Occasionally I would find one missing only to discover they had been killed overnight and partially eaten...it was very sad. Hamsters are very territorial and even the babies who had been handled since about a week old began to get aggressive, needless to say I ended up selling the survivors to the local pet store as I could stand to have this going on any more. No matter how much I kept seperating they just didnt enjoy any company really...They had large cages, and I had some other cages to seperate them into when some were getting bullied, nothing worked. Good luck and be sure to watch for bites.
Missing being a pet parent, but will be again some day when the situation allows it...Rest in Peace Willow my aussie girl-sept.19 2010, sweet Satin bunny Oct 1999-Jan 10 2006 and Tinsle chinchilla 2004-Jan.23 2008, Shiloh beagle dog June 23rd 1994-April 17th 2008, Grace chinchilla Dec. 26th 2003 -July 2008, Kit chihuahua Dec 1997-2009.