Is it discrimination when a boss kicks you out of a position to hire a younger person?

This company is brand new to our area, only been open for a little over a month. I was hired in to be there before opening and been there since. (It is a truck stop with an Arbys inside) I started out on the gas and diseal side, then my manager told me that since my hubbys works there too(wasn't a problem in the beginning) then I would have to transfer to Arbys side if I want to keep hours and keep my job.(He said they had to get rid of 3 people because they were cutting hours and couldn't keep them) So me and another girl, who is MY AGE, were moved to Arbys...unwilling. Then I walked in today to see that a girl that was hired in the beginning but called off one night and a no show the next night, WAS WORKING on the gas side! She is probably about 20 years old. Now, if there are NO hours, then how did she get hired back? It seems to me that the manager (who is 30) favors and prefers the younger workers. And the way it looks is he is trying to make us quit by moving us to Arbys side. He claims he didn't want to loose us and thats why he offered us the Arbys position, but there are other YOUNGER girls there that DO NOT do their jobs and they got to stay where they are. I should be thankful to have a job, but it is not the job I wanted or applied for. and it just irritates me that the ones that don't do what there supppose to do are the ones who are getting favored! AND THEY ARE ALL YOUNGER! Please enlighten me and tell me that this is discrimination and that there is something I can do. Thanks!