The way I handle roosting is to let them decide when they want to. Many people on this forum want to teach their chicks to roost quite early, nothing wrong with that. Many broody hens teach their chicks to roost pretty early. I just don't feel the need.
For my brooder raised chicks with no adults around most broods start to roost around 10 to 12 weeks of age. I don't teach them, I let them decide. I've had some start as early as 5 weeks, some go longer than 12, but 10 to 12 is fairly typical. How that coop and the roosts are built could have an effect on when they start, some of it is just their personalities. Yes, they do play on them during the day so they can get up there, but they just don't want to sleep up there at night.
If my brooder raised chicks are in the main coop with the adults, the pullets typically do not sleep on the main roosts with the adults until they are mature enough to join the pecking order, usually about the time they start to lay. It's not so much that they force their way into the pecking order, more that the adult hens seem to accept them as adults once they start to lay. There is usually very little violence. With cockerels, who knows when they start to sleep on the main roosts with the adults. It could be early or late.
I let my broody hens decide when they take their chicks to the roost. Until they take them to the roosts they sleep on the coop floor. I've had a hen take her chicks to the roost at two weeks, I've had some not take their chicks to the roost at all before they weaned them. Most of my broody hens tend to take their chicks to the roosts around 4 to 5 weeks of age.