When I bought my chicks, they told me I'd get eggs when they were 4 months old, but I think that is the highly optimistic perspective. I have a flock of 8 hens, 4 are 6 months old, 2 are just shy of that, and 2 are 5 1/2 months old. I got my very first eggs yesterday. Realistically expect sometime between 5 and 6 months of age to see your first eggs. (The first to lay eggs was the Rhode Island Red, one of the younger ones at 5 1/2 months)
I got my BO as a chick in mid-May of last year. She just started laying 3 weeks ago. That's 8 and a half months old. Really slow, I know. Hang in there.