I concur with most of what has been written. Those breeds would be expected to lay by about 20-24 week if reaching that age in spring or summer. If they reach that age between summer and winter solstice (declining day length), all bets are off.
The best indicator of the ability and maturity to lay eggs is the space between pelvic bones.
Red enlarge combs and wattles is a good indicator but I had an Orpington hen that laid well but had a small pale comb her whole life.
I have a hen now that has a huge bright red comb but she molted a couple months ago and hasn't laid since.
I don't put much stock into squatting as an indicator. Squatting is a desire to mate on the part of the hen, not that laying is imminent. After hundreds of layers, I haven't had a hen squat for me in years. (likely because roosters run with each flock)