I would say 19 months could be a little early--but I also think that every child/parents are going to have different experiences with this. My daughter started around that time to recognize when she needed to poo, and was also going pee in the potty around 2 years fairly consistently.
What we did was this: when it seemed like she was interested in using her little potty, we gave her opportunities to do so (she never handed us diapers). Pretty soon she figured out when she needed to poo (I don't think she liked having that in her diaper, some of her friends were the opposite and peed first). Then we gave her some time outside and in the kitchen without a diaper because we thought maybe she was ready. This did seem to get her started using the potty for pee and poo.
On her 2nd birthday she had gone a week without an accident. Two months later she started having fairly regular accidents (pee only). We kept her in underwear, because we wanted her to feel like she had "made the switch"--but we had to put up with a lot of clean ups.
By two years, 8 months, the accidents were getting to be fairly predictable (and therefore avoidable). This was around the same time that many of her friends started really using the potty.
If I had to do it over, I might have made the switch out of diapers a little later. In the end, however, it may have been good because she fully trained by the time her baby sister came along; and I think if she hadn't been, she would have regressed.
That's my experience.