Is there a way (with the fair queues) to give priority to new traffic over old traffic… either limiting the old long running download when something else wants bandwidth, or reducing a long running download to X bits/second when it has been running for Y time?
http://wiki.mikrotik.com/wiki/Manual:IP/Firewall/Mangle
You can’t match on how long the connection has been established, but you can mark based on bytes transferred in the connection as well as the connection rate. If you search the wiki and forums for those matchers you will find plenty of examples.