What is best age range to train baby to sleep by her/himself? Anyone has recommendation?

I wouldn't call it training. For my child, it's more of establishing a routine which she can fall into. Her evening bath is around 6pm and her last feed is around 10pm where she is coaxed to sleep. She used to wake up for night feeds, but can now sleep through the night and only wakes up at about 7am. Most babies can soothe themselves to sleep. My baby shakes her head from side to side when lying down. It looks really strange but she dozes off soon after she does that. She also sucks on her thumb to sleep.