How to tell if female is mature?

[MissHarlen]

My Aphonopelma seemani just molted into her adult colors and the molt has well developed spermatheca. How do I know when she is matured ebough to breed?

 

[sdsnybny]

When her spermatheca are fully scelortized (dark)

 

[MissHarlen]

When her spermatheca are fully scelortized (dark)

http://arachnoboards.com/gallery/look-at-that.42286/

Like this? This is the pic I took of her molt

 

[sdsnybny]

http://arachnoboards.com/gallery/look-at-that.42286/

Like this? This is the pic I took of her molt

Those are developed but she may not be mature enough to breed yet.
check this thread out. they should be very dark brown to almost black on a fully mature female. Younger females may produce a sac but smaller and sometimes it is to hard on their body.
http://www.tarantulaforum.com/threads/how-to-sex-your-tarantula.281/

 

[The Grym Reaper]

It's to my understanding that if they are over 75% of max leg span for the species and have sclerotised spermathecae (as @sdsnybny mentioned) then they can be bred.