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.