It is not uncommon for them to fight as they get older and become territorial. I think you should persevere with yours Matty and hopefully they will stay together. If they draw blood you will need to separate.
With an older single hamster trying to introduce a new partner can be very difficult and more often than not ends in fighting and separation. This often happens even with littermate pairs.
If you really want to try start by rubbing their scents over your hands then over each other. Next swap cages so the scents mix. Since you will only have just got one of them this may be stressful as it will not have had a chance to settle or be tamed yet so watch them for signs of illness. Then you can let them meet but they must be supervised constantly.
Always handle both, one at a time if need be, never only one as they need the mixed scents. Have gardening gloves ready in case they fight. Gradually leave them longer and longer together. As they mature they may become territorial and fight so watch them very carefully. The cages should have two of everything. Never feed in bowls, always scatter food on the floor as they can get territorial over bowls. Never do full cage cleans as you can lose their scents. Do half and mix the old stuff in to keep the scent of both in the cage. As you will realise scent is they key and is all important to our little friends!
Matty you should follow these rules with your pair that are already together regarding no bowls and half cleans to keep the scent in place.
It would probably have been wiser to have got a litter mate as they tend to live together better but you can but try so good luck. Remember you must always keep an emergency cage or bin available in case you need to separate quickly. Good luck