TexasCHLforum.com

This could open a big can of worms. If the minimum age requirement for getting a TX CHL applies to out-of-state licenses in TX, does that mean the other eligibility criteria apply as well? That could defeat the idea of getting another state's license because of not qualifying for a TX license. Would someone who is ineligible for a TX CHL because of convictions but qualifies for another state's license be ineligible for reciprocity?

I emailed DPS because the FAQ on the CHL web site appears to be based on the old 6-month valid period for CHL-100s.

Me wrote:The FAQ on the DPS website states:
"It is best not to take the course more than six months before your 21st birthday so that your proficiency certificate is current. Your application may not be turned in to the DPS until your 21st birthday."
With the proficiency certificate now valid for two years for an original CHL, can a student now take the training up to two years before his 21st birthday?

And the response:

DPS wrote:The CHL 100 for originals is good for 2 years indeed and if the applicant is not 21 years old yet he can take the class earlier than 6 months but then he’ll have to submit all the paper work when he turns 21, like you said.
With the renewals the CHL 100 is good only for 6 months.

So it appears you can take the class earlier, as long as you CHL-100 is less than 2 years old when you submit your app after your 21st birthday.
But I wonder why one would take the class so early, especially with the likelihood of laws changing this year. Further, the class requirement could change between now and your 21st birthday.