It depends
, if you have children/partner and need to be in a particular place then neither are easy options as you will have to travel both during the course and afterwards for training places .
if you have fixed financial outgoings that you have to pay , then this is going to be difficult as if you haven’t already done a degree you will be £100,000 plus in debt at end of course and will not be able to work during courses to bring money in . If you’ve already done a degree the money situation will be even worse . Graduating at an older age you will probably be paying student loan off for all your working life.
if you are wanting to do medicine/dentistry for better money , there are far easier and quicker ways to earn a good wage and even better pay with less stress
if you have struggled to get the academic qualifications , the course for both medicine and dentistry is a considerable jump up from A levels etc and very intensive
I have both interviewed people applying for dentistry as mature students and been a foundation trainer for new dentists some of whom had previous degrees eg pharmacy , biochemistry . I have also counselled medical colleagues who have started their degrees in their thirties and are struggling on qualification.
Many of the mature students had unrealistic expectations of earnings potential , working hours and the inflexibility of course and foundation year to fit around family/partner commitments . The same goes for some of the foundation dentists who were expecting an easier ride than their previous careers and are often surprised at the stresses of working in dentistry and that the financial rewards are not what they are expecting particularly after accumulating so much debt and with very large payments .
Both medicine and dentistry can be done in your 30s but you have to be an exceptional person , both to get in , but most particularly to tie yourself in your thirties to the uncertainties that the course and early years of these careers involve and the demands on your body and emotions . Your family , if you have one, will very much take second place for years and that is something else you have to think of. Do not contemplate if you cannot handle stress well .