Advice on problems related to buying flat in 49yr old chinese walk up

Am interested in buying a specific flat in Sheung Wan-however the building is 49yrs old...(lease is until 2063). I went to HSBC and they point blank said they do not offer mortgages on buildings of this age due to problems/resale value etc...(flat asking price is 2.9mill they value property at 1.9mill!!) I am aware other banks will offer a mortgage as long as i can put down sufficient cash. However, after my hsbc 'chat' i am now a little cautious that maybe buying into such an old building would not be so wise. Any advice would be much appreciated. Are there any specifics i need to look into? I intend to buy to live in, at least for a few years but, as with so many, i hope this purchase to be a future investment.