aggressive aging comes in when you are about to reach the size of the session table then the FW calculate which sessions to delete from the session table to free it up.
1) check that the session table is automatic / static
2) check the session table peak "fw tab -t connections -s"
3) check the TCP ports that you see that cause you the "asymetric traffic drops"
4) configure special service for them and you can disable aggressive aging / play around with the timers / check the values on the connection table on an live session / check logs for the delta between the drop log and the correlated log of the session start. ** most important disable the "match for any"
5) create a rule between the relevant source and destination with this new special service and verify that the traffic hit this rule.
6) now give it a time , and monitor the application & FW resources and modify that special rule according to the findings