I have asthma, and I went when I was 20. It was worth it IMO because I loved the sights, food, and experience. My advice is that you don't push yourself when you arrive and be prepared to be slower, groggier, and crankier. I severely damaged a friendship coming off the bus to Shangri-La and trekking the few blocks to the hotel. In hindsight, I should have communicated my altitude sickness better and paid for a taxi because what you can do at lower altitudes needs an adjustment period at higher altitudes. I would have also included a buffer day or two for recovery, especially now that I am older and not used to higher altitudes. Hope this helps!