My friend it is never too late.
Online can be harsh - but the vast majority of people are only average. I've been playing for years, and I'm only average - it's not really about experience, since most FPS games all handle differently, and only some things (like tactics, teamwork, reaction) carry over between games. Being able to aim with the sticks isn't the be all and end all. I'm a PC gamer, but ocasionally I play at a friends place, and they'll have an xbox or ps3 - but still I can win a game or two, by not relying on pin-point accuracy.
Perhaps also playing games like Battlefield Bad Company 2 would help. Class based team games allow you to specialise and focus on supporting(medic, ammo guy, spotter, turret on a tank etc.) a team instead of competing with everyone around you.
The more experience you have with FPS games the faster you'll pick up a new game, apart from that, it's a level playing field.
With Codblops however the game style is the same as cod4, codwow and modern warefare2 (because the engine is the same, the feel/pace of the game will be the same in most cases) - so codblops might be worth a miss if you're worried about being shot in every location =S
On the other hand - cod multiplayer doesn't care about how often you die - you don't lose experience points by dying - you can only gain them. So you'll progress up the levels depending on how often you play.
Someone already mentioned cooperative gameplay - That is a fantastic way to play shooters. Why not pick up a copy of Left for Dead 2 and play with some buddies?
My recommendations for your ps3 would be valve games (half-life/team fortress 2/portal/left for dead). If youre going to get into FPS games, might as well start with the best.
Like I mentioned earlier - Battlefield Bad Company 2 is great for new players (and if you get into the high paced shooty shooty part of it you can get Medal of Honor - it uses the same engine (same feel), but small enclosed maps and focuses on gunfights rather than big environmental stuff. Giving it a faster pace more arena style pace.)
I'm afraid I don't know anything about MAG. (I'm a PC gamer remembar?!)
Most important when getting into a new genre like FPS games? Play with your friends. If all your friends are only playing Codblops - get codblops... no point in buying Team Fortress 2 if none of your friends have it =S.
Always try to join in games with friends - it makes games 1000 times better.
I hope all that helped.
