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

Start as early as possible, and get into a routine and stick to it everyday. Your baby will soon recognize the signs and know that its time to sleep/nap. For me, this is how my schedule is like for my son. He wakes up at about 6 - 7am in the morning, plays for about 2,3 hours before putting him in his bouncer for nap. Nap varies from 15 to 30mons. He plays for an hour while my mother prepare his meal, and approz. 1.5 it'd bath time and nap again in his bouncer. Wake up and a short nap 2 hours later, and he will be up at the way until I come home. I'll play with him for a little while, then I'll wipe him down and change him to his PJs. Massage him and by now he knows it's bedtime. I carry him to our bed (we co-sleep), let him lie on his side, pat his bum for a few minutes and he's gone for the night until tomorrow 6 to 7am.