Your son is definitely ready. Pay no mind to anyone who tells you that you have to wait. You don't. Just be supportive, don't expect to train him 100% over a weekend (expect more gradual progress, but every pee/poop in the potty is a diaper saved and one more step in the right direction), and remain relaxed and loving and work as a team.
The easiest way for you to help him learn the connection between what comes out needs to go in the potty is to:
1) remove the diaper
2) relax about the temporary messes (whether that means hanging out in one safe room for a while, rolling up carpets, doing extra loads of laundry together) and be supportive and talk about what's happening
3) let him experience pee/poop coming out (without the diaper, preferably without any butt covering, though plain undies is better than anything waterproof)
4) once he knows the sensations that come right before the pee/poop coming out, sitting on the potty will be a no-brainer - hit your local dollar store for a few little plastic potties and keep them close by you during this period of time, gently suggest the potty but remain relaxed, no-stress, no-pressure
5) definitely always have him accompany you to the bathroom and "just try to go while mommmy/daddy goes" - you don't have to go, but you do have to try
This is the shortcut - the more waterproofing you have on him, the longer it will take (in most cases). It does involve potentially some accidents, but NEVER crying or forcing or punishment. Those are BIG no no's. The accidents are simply valuable learning lessons for both of you, really - for him (so that he can connect the sensation of having to pee/poop with the result, and then when he knows that, he can get pretty quickly learn how to get himself to the potty in time) and for you (so you can offer him the potty at an optimal time and support his learning).
Don't let anyone dissuade you with "boys potty train later" and "most kids don't potty train until 3 yrs old" -- these are all cultural expectations, not physiological truths. The reason why so many kids only want to poop in their diaper is that it is the place WE (the parents) have trained them to go for the past 2-3 yrs. The longer they poop in their diaper, the less interested they are in switching to the potty. So you can certainly wait, but just know that it's super common for these kids to pee in the potty but ask for a diaper when it's time to poop. There is another, low-stress, loving, pressure-free way. In fact, your 3 month old can use the potty too (it's amazing, NO stress, and far easier than you'd ever think, and *much* better than dealing w/ blowout poopy diapers!), and to have the 2 boys using the potty together is wonderful motivation for your 2 yr old - check out:
http://www.diaperfreebaby.org/Articles/GettingStartedBobr...
http://www.diaperfreebaby.org/PottyingPositions.htm
http://viviente.com/2005/10/how_to_do_parttime_pottytrain...
Happy pottying!