My Male Guinea Pigs Behavior

Question
I bought a Guinea Pig (Charlie) about 4 months ago and I decided that he needed a friend since I have to work now. The Guinea Pig I brought is about half his size and all Charlie tries to do is mount him (Rascal). When they are inside their house which is an igloo, they are fine and they are usually relaxing beside each other. Every once in awhile Charlie will chase Rascal around the igloo and try to mount him. When they are outside the igloo, Charlie tries to mount Rascal a lot. What should I do? I know that mounting is a form of one Guinea Pig showing dominance to another Guinea Pig but that's all I know. Will this behavior stop or will I have to take the little one back? I really don't want to take Rascal back to the pet store but I don't want Charlie to hurt him.

How can I tell how old he is? He looks like an adult rat with hair (only cuter). I think that he is still a baby because of his size but, I know that the pet store wouldn't sell me a baby. Please respond back. Thank You.   

P.S.
They are indoor Guines Pigs.

Answer
Carolyn,

Charlie and Rascal are showing normal behavior. Because Charlie is older he will most likely be the Alpha. Charlie will stop mounting Rascal pretty soon. Charlie won't hurt Rascal, this is totally normal behavior. Males tend to go through the dominance behavior longer then females. There is nothing to worry about, as long as there is no signs of aggression toward each other, and just the mounting and head raising then they'll be fine and nothing for you to worry about. All this will pass fairly soon. :)

I would say Rascal is about 6 weeks old. Before you freak out, the pet stores sell Guinea Pigs from the ages of 5 weeks to about a year old. Rascal will start growing really fast here soon. Guinea Pigs reach their full length by the age of 1 years old. There isn't really anyway to tell how old Rascal is for sure, but since he is about the size of an adult rat then I would say he is about 6 weeks old. Guinea Pigs are ready to leave their mothers by about 4 or 5 weeks old. So there is nothing to worry about in his age, though I would recommend that you feed Rascal a mix of alpha and hay as this will provide better nutrition for him.

Hope this helps, everything will work out by the end of the month no later then early next month. Just spend as much time as you can with both of them and everything will work out fine.
                      Jules