DD4 read her first word in front of me when she was 2.5. Right before she turned 3, she was reading some words and trying more. She is 4.5 and can read chapter books. It seems that it was gradual and then suddenly accelerated.

She is very verbal, but she is more math and physics oriented. She was not an early talker, but when she started, she zoomed. When she was about 20 months, people really noticed her verbal abilities, her clarity in speaking and her vocabulary was strong. And the reading was similar in the way she tackled it.
Slow, and then zoomed.

Ren