Originally Posted by stephenlovatt
Not sure how old as we got her as an adult, about 18 months at a guess.
Hmmm, i think maybe someone was lying to you, females mature between 5 and 8 years of age and males 3 to 5 years roughly, source: AQUA-TERRA-VITA: Caring for your Mexican Red-Knee Tarantulas (Brachypelma smithi)
I questioned the age and sex because when an adult male goes into a shed the pedipalps and the tibial spurs (the "hook" like things on the front legs) can get stuck which kills it.
Chances are tho the humidity isn't high enough so the skin is stuck to it. Try mist spraying him/her, if it twitches its alive, it not the probability is high that its dead. The mist spray will most defo help it shed if its alive.
Hope this helps