after Master Hospital administration can i do doctor's degree (PHD)
Yes, you certainly can. MHA is a Master's degree and like after every Master's degree, you can pursue Ph.D. Now most of the Universities do not have any upper age limit. There are Universities that offer part time Ph.D as well. And there are Universities that offer Integrated programmes too. You can choose Clinical Research, Supply Chain Management, Logistics, any of the specialisations related to Health care to pursue Ph.D