Answer 1

It really doesn't matter how old you are. If you want to learn a programming language then go ahead, it's never too late for that.
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Answer 2

voja's answer is completely correct.
But i still think it's good to point out that in some languages (i.e. COBOL) it will be harder for younger people to get better jobs. Most of those are "oldies" though.

Answer 3

yes, low limit is about 9-11 years for very basic of some common prg. language. Children need understsnd variable concept, read, write and basic of calculate.
But there are some easy languages suitable for learn kids. like logo, scratch, karel, or there are games too with algorithmic works hiden in adventure.

Answer 4

no it doesn't matter that how old are you what is this you can learn programming at any age