I personally started when my boy was 9 weeks old(a week after I brought him home). He would be passed out sleeping on his side, and I'd trim all of his nails. And I always play with his feet, even now. Every week I'd do something with his feet, and his back ones usually need some sort of trimming. Sometimes, I'll just trim one foot, then wait a few days to do the other foot. Not because he was struggling, but so I can handle them more often. Once he passed the baby sleeping unconscious stage, he remained to be good with his feet.
My belief, is that starting young like that, he'll get used to it and know that it's no big deal. And now it's pretty easy to trim his nails, he's really good with his back ones. It's just a matter of keeping him from walking off, but he doesn't care that I'm holding his foot. It's the same with the front ones, he just wonders why he can't walk :lol: and sniffs at the nail clippers.
So if you have a baby, I'd take advantage of the sleeping and start working with their feet. Even if you don't trim it, rub it gently between your fingers so they get used to handling.