It’s a good sign, but no, it is not necessarily a sign that they are ready to lay. I’m assuming they are adolescents.
The mating act is not just about sex. It is also about dominance, especially when the hormones kick in with young cockerels. The one on top dominates the one on bottom, whether that is willingly or through force. The cockerel’s hormones are telling it to dominate the flock so it can be flock master.
Normally the cockerels mature earlier than the pullets. The pullets’ hormones don’t necessarily kick in until they are ready to lay. Until then they are more likely to resist the advances of the cockerel and try to run away rather than submit. The cockerel also needs to impress them that he is a worth mate before some of them submit. Adolescent cockerels may have trouble impressing them.
If the pullets are willingly submitting to the cockerel it is even more of a strong sign that they are getting ready to lay. It’s still not a guarantee, some will submit to a cockerel at a very young age. I’ve had a 13 week old pullet submit to a 13 week old cockerel and she did not lay for another two months.
It is a sign that they are maturing so I’d get the nests open and ready for them, but you may still have a wait. Good luck with it.