As long as senior primary school. As long as high school. All of my years of university.
Today it has been five years since I said goodbye to the only home I ever knew; a planet in the southern arm of the African galaxy; to float over seas and space in the Great Abroad.
If we can't go interstellar, we go international (at least for now). Holidays give brief glimpses beyond the horizon; offering short, tethered spacewalks into new worlds. We've all seen these places on TV, in books, or online. Some of us have even been there a few times.
Never let the relative convenience of modern travel lessen the magnitude of this fact: you are still in a one-person spaceship (to paraphrase Canadian astronaut Chris Hadfield) and that is yourself.
When you board a plane, train, or just break free of the country you may call 'home' at this moment, you are slipping the bonds of familiarity for something that can be truly out-of-your-world. You are carrying all you can (should?) need to sustain your life in this alien environment. Whether it's the Moon or Monaco: if it's just for a few days, you pack light and don't forget your passport (or sun protection).
But what if you stay? What if that blue orb of your origin becomes yet another coordinate in the sky? One you may return to again, but just as another pit-stop on your journey through the stars?
In the hopefully not-too-distant future, the first men and women landing on other planets will probably look back at Earth with the same pang of homesickness that the first explorers of it must've felt crossing mountains and oceans to seek new places to call home (from).
We're not there yet, but perhaps we never are. For now Planet Earth is blue, and there's so much left to do. It's time to leave the capsule if you dare.