>>276
I think you forgot to put "き" between "行" and "4." "はじめて" is usually written as "初めて" in kanji. It's not wrong to use "始" in this meaning, but I think it's a bit old fashioned. Other than these, I think it's ok.
If you'd like to sound more natural, then you may want to omit "間" so it reads "4年が経ちました." I don't know why, but "4年間が経ちました" sounds slightly foreign.
This might be beyond JLPT level, but "Aに行きX年が経ちました" often implies "I have been in A for X years," i.e., you haven't returned to your home country for X years. To avoid ambiguity, you may say "Aに行ったときからX年が経ちました" or "Aに着いた(or 向かった)ときかからX年が経ちました."
The former wording fits in perfectly when you refer to a relatively short trip. If your stay was relatively long, its meaning becomes ambiguous because it literally means "X years have passed since an ARBITRARILY GIVEN day during the trip (the speaker doesn't specify when it exactly is)." So, it's better to avoid the wording when the stay was longer than, say, a year. If you used, the listener would most likely take it that you meant "since the last day of the trip" or possibly "since the first day of the trip."
The latter wording is always clear what you mean.
Finally, if I were you, I'd say "初めて日本行きの飛行機へ乗ってから4年がたちました." This may sound a bit poetic, but I like to use these kinds of expression when I write to a friend I haven't seen for years.