I have had a couple hens that did not lay until nearly a year old and go on to become good layers for years to come afterwards. That is not the norm but it happens. A couple have laid very early on as well and were never great layers. Just like children , all may be different in behavior and outcomes. I seldom give up in less than a year on a bird, except for severe deformity or illness that they likely will never recover from. A couple months or so, range is fairly typical between and even within breeds. Often, in a large brood, when a couple start laying it seems to spur the others on to lay and most start soon afterwards, just breed and environmental factors in regards to the timing likely. That is not always the case, however, and slow starters are common. Give them a chance if you can afford the feed.