When can you sex a Guppy/Are they sexually mature?

[Burks]

I have twelve, six week old Guppies in my tank. When can I successfully start to sex them so I can remove the females to the female only tank? When do they become sexually mature? I've read from three weeks to almost eight weeks.

I want to get these boys and girls apart quickly.

 

[Mudskipper]

From three to eight makes sense. There growth depends on there enviroment, food and genetics. What works with my endlers is if you feed them up a bit( makes them bulge ) then look for the "gravid spot" you can can usually see it on the females. BUt it is not a sure thing, one major sign is the males coloring up, and the flattening of their anal fin( gonopodium)