Like a full out tool attack may kill the bronze jumper, a full out bronze attack can kill a iron jumper too.
In recent days, I have tried to go iron rush - without almost no bronze millitary and ironed from 19-23 min with shang or other slow civs. I found it is really a bad idea to do so if your opponent is a decent good players.
I wonder how you other players do - make a bronze rush, then go iron (iron around 30 min) ? or make a full out attack in bronze until you feel that it is the time to go iron (which usually means iron after 40 min game time) ?
Once when my opponent was weak, I ironed around 19 min with shang, had 70 vills/boats (about half of each) and 5 docks - but I could not get 10 Scythe Chariots until 25 min in game - the major problem was wood - I think it is meanless to have 30-40 fishing boats - around 20 with 2 docks would be better. In this game, if my opponent attacked me 17-18 minutes in game with CAs + some camels/cavs - I would be dead as a stone.
Also, HAs are much better iron rush units than SC - one may be able to send 10 HAs into enemies town about 22 min in game - and if it is walled....
I do not think I will care about my iron time any more in future.