Post by lightclaw
Well, being old shouldn't keep you from improving. I'm in a guild where I'm one of the younger players at 34 - we've got grandparents who play well. We're not cutting edge raiding guild material by any stretch of the imagination, but we've also got the sense to not want to be.
Do you intend to play with your son, or has he just dangled the warcrack in front of you and gotten you hooked? If you're going to play together, he is probably in a guild, and hopefully knows a decent, patient paladin who can help you improve your game.
If not, post a message in general chat in a capital that you are looking for a guild that is mature and willing to help clueless people. You may not find it on your first try, but you can always /gquit and try again. Sure, you might get trolled (OK, you're going to get trolled) but you do what you've got to do. Try to find a paladin who plays reasonably often and ask for advice about gearing, rotation, and the like.
You're never going to be able to catch the twitchy, caffeine soaked, up-all-night 19 year old college kids, but you can definitely get good enough that you're not going to embarrass yourself. :-)
That said, I would suggest that you stick with ret until you're comfortable with it, then try tanking with an understanding group from your guild. As long as they know what they're getting into, they should be reasonably understanding when you screw up, which will happen. If you try to begin tanking by jumping right into it via the dungeon finder, you're setting yourself up to fail. It's possible to get a wonderful LFD group by chance, but it's far more likely that you'll wind up with a group that is in a hurry to finish so that they can get their daily valor and be on their way. They're not going to be interested in giving you tips for the fights, or throttling their dps/waiting to heal so that they don't pull threat off of you right off the bat, and the like.
Whatever pressure you might feel to keep your dps up is nothing compared to the pressure you get to maintain threat, deal with boss abilities, and stay alive as a tank. You also get far far far more buttons that you need to press.
I would also strongly suggest that you check out Noxxic's Ret Paladin PVE Guide
as well. It will help you figure out which stats you are looking for, gems/enchants, talents, glyphs, and your rotation. You might not get it all right, but you'll have a good source for information. It's targeted at level 90 paladins, but it should largely apply to those at lower levels as well.
Welcome to Wowhead, best of luck in your gaming. :-)