Im curious on this too... mainly cause i have started leaving Spock alone in the bath for short periods, eg while i go grab a glass of water or get her pjs. Ahe is now 27months. And i do keep her talking while im gone, encourage. Her to tell me a story or sing me a song.
Im curious if this is about the same age others did.
She does rarely have a bath on her own tho. Either i have a shower and put the plug in and she bathes too (our shower is over the bath) or i just have one with her