Introducing 2 male kittens from different litters

Hi there! Just looking for some advice please we have a 17 week old male ragdoll and after me and my partner having a chat we thought it would be good to get him a little friend. So last week my partner came home with a 10 week old male ragdoll/persian cross. We have separated, done scent swapping etc our oldest gave a few hisses then wasn't bothered and when it came to introducing our oldest baby gave a few hisses and wanted to play. We have separated them at night and do some short intervals of supervised interactions duribg the day. Our youngest loves to play with our oldest but the issue is our oldest is getting a bit too excited and a big aggressive with the biting so we separate them again.

Can anyone give advice are we doing this wrong? Thanks!