Man, I haven't played 1st person shooters since Rainbow 6 and Rouge Spear, America's Army, etc... Had kids, tired of endless PC upgrading.
So, for C'mas I got the kids an XBox and MW3 for myself... I swear I don't think my 43 year old brain and fingers are EVER gonna get used to that damned controller! I am getting SCHOOLED!
All I can say is keep at it, I am as old as you, and an old school WASD/mouse player as well. (ROT, DF Landwarrior, americas army, etc...)
and I felt the same way as you, but the console controller can be learned...
Little by little, I have improved and am finishing in the top 1/3 of the game rankings now..
Branch out to other games that require different button use. You will go back to all the FPS stuff and everything will be second nature. Biggest mistake I see alot of people make when going to a console is jumping on the MW2/Blackops/BF3 wagon and thats ALL they play. There are a metric shit ton of titles out there and some of them make those games look like kids stuff.
Playing an fps with a controller is like trying to drive a car using chopsticks. Console makers need to man up and go mouse and keyboard.
I am not nearly as good with the XBox controller, either. As a result I play most FPS on the PC.
There is one trick that works for me though- The "FPS Freek" stick extensions. I just put it one the right stick for aiming and it helps me make quicker and more precise shots.