I don't see any point in asking others that what age is best to make investment in bitcoin or any other assets because if you see the investment will give you return in some years then probably invest in it if you are not too old as you need some pension or saving plans to retire and enjoy your time period.
Frankly saying we don't know about the future and young age investment doesn't guarantee you will enjoy them in old age but still we make investment to some extent based on the age factor but you are still 28 and if you see bitcoin as investment with profitable return and understand why it will be giving return then without any doubts invest in it holding it for long term.But the main thing is you have the mindset rather then relying on what others have to say.
Frankly saying we don't know about the future and young age investment doesn't guarantee you will enjoy them in old age but still we make investment to some extent based on the age factor but you are still 28 and if you see bitcoin as investment with profitable return and understand why it will be giving return then without any doubts invest in it holding it for long term.But the main thing is you have the mindset rather then relying on what others have to say.
With this lifestyle, I don't think you'll last long. So it's too late for you. 
I see why has he put forward the age barrier related doubt now because this lifestyle will not be helpful even with bitcoin investment so the guy needs to change some habits.