things may change when they get older
but i have rules for mine and make them cool it when it gets too escalated , but thats my rules. they would get really rough if i dont step in and never would fight but i dont like them bullying each other if one doesnt look like they are enjoying it they take a break. most of the time they break on thier own. more noise the better it seems. its the quiet ones you have to be careful with.
also when dogs get tired they can be less tolerant .when one nips the other too hard you might have some bickering or a full blown fight. my dogs are close in age as well and in the same age bracket but my female is really good with other dogs and so far Rebel is below her.
when i fostered Shawty would play with another female they were a year apart they loved each other but could only play to a point they had to be watched closely sometimes they would bicker so the next step would be fight so i cut them off before anything bad happened they learned quickly what was allowed