Birds with rose/pea combs

[Glory to His name]

How/when can you tell they’re roos?

 

[JedJackson]

It varies but it's the same idea of watching for growth and color in the comb and wattles when they are young, under 14 weeks or so. Wyandotte females sometimes get bigger, colorful combs early. With them, you can look at the evenness of the lacing on the back, and the hackle color. Males tend to have patches at the shoulder and darker hackles, while females tend to have even lacing and lighter hackles. There's no one size fits all for judging gender.

 

[EggSighted4Life]

How/when can you tell they’re roos?

Depending on age and if they're a henny feathered breed like seabrite or not.. the saddle feathers will be gender specific.

The cockerels and roosters are still significantly larger/taller combed than the pullets and hens.. and will still turn fully red (not to be confused with temperature or excitement flushing) way before gender specific saddle feathers appear.. often between 6-8 weeks of age.

Example images from google.. starting as early as 10 weeks but more flowing like the second pic usually by around 16 ish weeks.

It wasn't easy to find comb comparison pics but some reference examples also from google..

 

[Glory to His name]

Thank you both!
The chicks in question are mixes, some from my Brahma and some from an EE.