Do boas really grow into 20ft monster or is 14ft a more realistic size and how long do they rake to grow to sexual maturity ready to breed and how big would the enclosure need to be to keep an adult

It depends on what boa species youre talking about, is it male or female? Females get bigger then males with most specie of boa the male wont reach larger then 7 feet....females range from 8-12 feet.

i am just wondering cause I would like one but I was worried where I was going to put a 20ft snake if you get my driftwood

Check out the Herpcenter caresheet about the common boa: http://www.herphabitats.com/reptile_...common_boa.htm
Probably it has the answers to most of your questions.

There are many many types of boas, I assume you're asking about the common boa. Generally males will always be somewhat smaller. My sister had a female Red Tailed boa that got over 10ft.
It's definitely a VERY good idea to think about where you will house and how you will care for the adult-sized animal. Boas can live up to 25 years, so you are very smart to be thinking into the future.

There are no 20 ft long boas! You are thinking about pythons, Burmese retics etc.
Even at 10-12 ft this is still a good sized snake and will require a lot of space as well as an fairly decent amount of food.

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Merlin,
What's Life Without A Little Magic!

I agree and be sure to play it safe and have someone around when handling a snake of that size.....

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Warmest Regards from Lyn