Hi there and welcome to the forum!
well first off, in order to being issued an ATPL one needs a minimum of 1500 hours total flight time experience. Which usually nobody can afford paying for, unless money doesn't really matter to you since you got plenty of it. Usually once you are finished with flight training you're issued a CPL/IR (with ATP theory credit in Europe, commonly referred to as "frozen" ATPL, there is no such thing in the US) and then you usually work you're way up the latter, as a commercial pilot to accumulate the required flight time. There are various ways to do that, depending in which part of the world you live, meaning where you have the legal right to live and work, to make a long story short!
Regarding your medical question, before taking any action I'd strongly recommend to go and see an AME (Aviation Medical Examiner) or post your question in the "Medical & Health" section here on the forum.
Here a list of FAA (US) AME's in Hong Kong (I'd suggest to get it cleared if you'd qualify for a 1st class medical):
Find an Aviation Medical Examiner (AME)
Secondly, where do you intend to get your pilot license, Europe or US? I'd strongly advise going the US way, since it far less hassle. Meaning, it's much more hands-on experience oriented, less time consuming and less expensive as it would be in Europe! As a Non-EU citizen it's absolutely pointless going for a EU (EASA) license! You won't get any work, no EU airline or operator will hire you, unless you have the unrestricted work and residence permit. And from an international point of view, there is absolutely no difference between a FAA (US) and EASA license, both are equally recognized and accepted!
As you've probably noticed by now, I'm a strong supporter of the FAA (US) system. Reason being I've experienced both sides of the coin, meaning I know both system quite well, FAA and EASA. I received my flight training in the US (PPL up to CPL/IR and Flight Instructor as well) I spend a few years working in the US as a CFI (instructor) and by no means I want to miss this experience! Currently I'm in the final stage of the "conversion" of my license form FAA to EASA, which basically means in the end I'll have two pilot licenses, FAA and EASA.
Regarding the question about the time frame, that's difficult to say since there are so many factors which come into play, like personality, motivation, financial situation, time available etc. But in general it can be said that the US path is usually the faster one. In the US we are talking about a time frame of approximately 6 -12 month, full time course (PPL to CPL/IR). In Europe that's the time frame for the ATP theory studies only, provided you're attending a full time ground school and/or are really dedicated to your studies. If you're going the modular way (meaning distance learning) this can easily extend up to 24 month and more.
Since you're from Hong Kong, you might want to be looking at countries like Australia or South Africa for flight training as well. Hope I could help and good luck!
PS. check out the following links, perhaps they contain some useful information:
https://en.wikipedia.org/wiki/Pilot_..._certification
http://www.faa.gov/regulations_polic...uals/aviation/ (recommend "Pilot's Handbook of Aeronautical Knowledge)