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You are getting some decent advice here. A rooster makes absolutley no difference as to whether they lay or not. Golf balls do not get them to start laying. They just encourage them to lay where you want them to lay. Layer feed contains everything they need to lay good eggs. Feeding them extra calcium, like in oyster shell, will not encourage them to lay. They should be getting all the calcium they need from the layer. If your eggs have thin shells, offering oyster shell free choice is a good idea, but if your egg shells are thick enough when they start laying, feeding it is really just a waste. It does not hurt anything and it seems to make a lot of people feel better to feed oyster shell, but if the egg shells are thick enough, the chickens really don't care.
Chickens are all different with individual personalities and rates of development. No one can tell you exactly when they will start to lay. My first one started at 18 weeks. (23 pullets total) Two more started at 20 weeks. Two more started at 23 weeks. Several waited a lot longer to start. When they start depends on heredity, health, stress level, nutrition, and other things. How they are fed while they are quite young can make a difference in their laying. Everybody is real anxious to get that first egg. I was too. And with 9 leghorns 25 weeks old, I'm not shocked but a little surprised you have not seen a few. As anxious as I was for that first egg, I think we are really better off if they delay laying until their bodies really mature enough to lay eggs safely. My one that started at 18 weeks did not make it to my permanent laying/breeding flock. Her egg laying system never did straighten out the way it should have. At 25 weeks, though, your leghorns should be beyond that problem.
The rule of thumb on this site is that you need 4 square feet of space for each chicken in the coop and 10 square feet per chicken in the run. There are a whole lot of assumptions in that rule of thumb. It is intended to keep everyone out of trouble from Anchorage Alaska to Miami Florida, from Phoenix Arizona to Little Rock Arkansas, from Cape Town South Africa to Inverness Scotland. It is supposed to cover three chickens kept in a big city back yard to someone living in the wide open spaces with a large flock. One of the big reasons for that much space is the assumption that your chickens will spend several days in a row locked in the coop without even being able to go outside into the run. That is often due to winter weather but there are lots of other things that could cause that. If your chickens free range outside every day and are not locked up in the coop for long periods of time, your 4x5 coop is probably big enough. It would be even better if you feed and water outside, but that is mostly so you can give them enough room for nesting boxes and roosting without them roosting over the food and water, fouling it with their droppings. If you do leave them locked up in there for extended periods of time, yes, your space may be too small. We all have different circumstances and requirements.
I advise patience. They should start real soon.
Good luck!
