I'm not enthusiastic about sleep training either - the gradual, controlled removal of sleep time emotional support by the parent. I would suggest to be very conservative and cautious if you want to take that route, and as the article states, definitely not before the age of 6 months.
Edit: I saw another comment which talked about "checking in" on the infant during sleep training. I think there is some middle ground I would be comfortable with after 6 months of age, where you don't rock the child to sleep for an hour, but you check in on them, gently touch them, talk to them soothingly for a little bit, and then you leave them for a little while. Come back in a little bit and briefly soothe them, and then leave again for a little while. As long as they know you are there. And you could stretch those periods out to see how the child does. But, again I would suggest to be very conservative and cautious and don't try this at too early of an age.