S.,
Of course it is fine to start helping your son to the potty. The great myth of "potty training readiness" is an interesting one. In many parts of the world, infants are held over a potty from birth. This method is often called Elimination Communication or Infant Potty Training. Only with the advent of cheap, disposable, super-absorbent diapers have we been able to put potty training off for years on end. The idea that children develop bowel/bladder control is pure medical myth. There is absolutely no scientific evidence that this is true - it is simply something that has been repeated and taught, and everyone believes it. Again, the majority of children in the world do not have diapers and they do not soil either themselves or their mothers. Many of our grandmothers will tell us that their kids were potty trained by a year of age, but our generation brushes it off as an impossibility.
The concept that a child will regress or be emotionally scarred from early potty training is tied to the forcible training that was done in the 50's. Children were literally strapped to a potty chair until they "produced." Many mothers were even told to go so far as to give their children daily enema's to "train" their bowels to move on schedule. Yes, that is horrible and scarring, but it bears absolutely no resemblance to you lovingly responding to your son's desire not to soil himself.
Trust your gut. If your son is interested, then give him opportunities to sit on the potty. People seem to have this idea that it's not "real" potty training until your kids walk to the potty, pull down their pants, produce, wipe and redress. If you are putting your son on the potty and he gets it in there, who cares about the semantics? Just don't push try to force him when he doesn't want to. If you google EC or IPT, you should get some great websites. Many of them have sections for starting out with older infants. No matter what, just remember to follow your son's lead. If he is aware and willing to try for the potty, then help him. If he decides he isn't interested, then don't push. It will all work out fine.
Best of luck,
S.