How often do you use Future Perfect in the US and UK? How does it sound to you?
I will have visited Asia by the time I am 30 years old.
The mankind will have colonized Mars by 2030.
For example:
a) We use it (regularly, seldom).
b) We don't use it but it sounds nice.
c) We don't use it and it sounds awkward.
We use it when we need it, and don't really notice.
But it is not clearly needed in either of your examples. Simple predictions are ordinarily expressed with a will + infinitive future:
I will visit Asia by the time I am 30.
Mankind will colonize Mars by 2030. (Incidentally: no article with mankind)
But if your context establishes that such an event acts as 'background' for some other predicted event, a future perfect construction is called for. For instance:
I will have visited Asia and be ready to start writing my book about it by the time I am 30.
The only hope for the survival of the species is that mankind will have colonized Mars by the time our oil reserves run out in 2030.
You only use the future perfect if your story includes some future event—not just a date—to which the fp event is necessarily anterior.
I don't know that there's much difference between US/UK here, but for the record I'm from the US.
I think your two examples are perfect, so let me use those to explain:
I will have visited Asia by the time I am 30 years old.
I wouldn't say will have here. I might intend to visit Asia, or hope to visit Asia, but I can't be sure I will actually do it. It is something that I personally wish for myself, but can't really be sure will happen. As such, will have sounds strange here. The only time I can think it would be natural to use will have in this sentence is in a scenario like this:
Person A: "You're turning 30 in a week, there's no way you can plan a trip to Asia by then!"
Person B: "You're wrong! I will have visited Asia by the time I am 30 years old!"
In this case there's a stress on will; you say I can't, but I say I will do it. But even in this case I think other alternatives are more likely; I don't think will have is used very often at all when talking about things you wish to personally accomplish. It's perfectly grammatical, and you would be understood, but it's not really something we say.
On the other hand, take your second example (and as an aside, note that it is simply mankind and not the mankind):
Mankind will have colonized Mars by 2030.
Statements like this are much more common. When we're talking about things outside of ourselves, especially things which are projected to happen by some sort of data, we're more sure of the outcome and thus more likely to say it will happen. For example, you might say:
NASA's program for the coming years includes plans that mankind will have colonized Mars by 2030.
If NASA is telling you it plans to do something, you're much more sure that it will happen than a dream you have to visit somewhere by a certain time. So we're more likely to use will have here because we have a higher degree of certainty that it will happen.
That said, if I were writing the sentence I think I'd still be more likely to say:
NASA's program for the coming years includes plans that mankind will colonize Mars by 2030.
I'm perfectly comfortable with will have, I just think I'd be more likely to use will alone. As others have said elsewhere on the site, we don't tend to use perfect tenses unless we have to. If we can get the same meaning across without it, often native speakers won't use it.
