At what age would you say its easy to confidently say hen or not?
Yours are already at the age when I would expect it to be easy
Some chickens mature at different rates. The ones who follow the usual pattern are fairly easy, but the ones at either extreme are hard. Fast-maturing females can be mis-identified as males, and slow-maturing males can be mis-identified as females. Unfortunately, when you have a bunch that are all the same kind, they can all be the same kind of exception (all of them being females that mature fast, or all of them being males that mature slowly.)
Laying an egg is a definite sign of a female.
Definite signs of a male would be crowing, or grow slender pointy saddle feathers (they grow on the back, and eventually get long enough to hand down on each side of the tail.)
If you are able to rehome the one in the first post (pretty obviously male), maybe you can check regularly with the person who gets him? When he grows obvious male saddle feathers, there is a good chance that all other males from this batch will have them too, and that any without those feathers will be female.
These chickens don't have enough space for 9 of them in my current run and I cannot expand. At the same time I don't want to rehome 5 just to find out some of the ones I keep turn out to be roos.
Yes, that is a tough situation.
You could rehome the most obvious males. That will make a bit more space for the rest while you figure them out.
You could rehome the 5 with the biggest & reddest combs, and keep the 4 with the smallest combs. If they are not female, neither are the ones who have even bigger/redder combs.
Or maybe pick one with a middle-sized comb and get a DNA sex test on it. Once you know for sure the gender of one bird, you know half of the others too (tested male means any with bigger/redder combs are also males, or tested female means any with smaller/paler combs are also females.)
https://iqbirdtesting.com/
