These are not burmese pythons...
Boas grow verrry slooowly...
First, it would take 5 - 10 years before your boa can reach its maximum size....
Do you really think this would be a problem in 5 - 10 years, if you even still have her at that time?
Second, most Boas don't reach the maximum size often described.
I've heard many times that a female can reach lengths of 12' - 14' long, and males at about 10' or so BUT I have YET to see a boa over 10 feet long in about 15 years.
I've got an 8 footer and a 9 footer that haven't seemed to grow an inch in over 2-3 years...
So if you really think about it, there isn't much difference, at least not something that would deter you from buying one, only to buy the other.
Considering that when boas are bred, the female typically is larger than the male, it would make more sense to buy a female now. This way, if you do decide to breed in the future, you have about 2-3 years or even more to find a suitable male.
Hope this helped.
Joe Rollo
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'Tis not the stongest of the species that will eventually survive, nor the most intelligent, but the one most responsive to change' Charles Darwin
Thanks and take care - Joe Rollo