Different aged roosters and hens have been kept in the same flock for thousands of years. They have developed behavioral methods for the species to continue.
They are living animals. No one can predict exactly how they will behave. It very much depends on the individual personality of the roosters involved. I think it also depends a lot on how much space they have. If you have been able to keep two roosters in the past with your conditions and set-up, you should be successful in the future.