Dd1 started consistently sleeping thru at around 4 months (7pm-7am with a 10pm DF, and I dropped the DF at 7 months). We never had any set backs until she was around 15m, but that was probably due to an overseas trip. Dd2 (4m yesterday) seems to be doing the same thing (last night she slept from 7pm - 6am with a 10pm DF). The early morning feed seemed to be getting later and later, the night before last it was at 4.40am. Both my daughters were/are not big, with my dd2 being smaller than dd1. A friend's (large) baby was sleeping til at least 5am (from 10.30pm ish) from 6 wks. I know she was doing 12 hr stretches before 3m. She was also only feeding 4hrly pretty much from the start!!
So yes, all babies are different.