sir,i want to go in research field in biology in aging .how can i go in this field
through mbbs or BSc in biology.what is the scope in this field

Both routes are options for a career in researching ageing/senescence. Which is best will depend a bit on the specifics of your interests. For instance, are you focussed only on humans and (for example) how research might improve human longevity (or quality of later life). If so a medical degree may be most appropriate. If however, you are interested in more "ultimate" questions  about why organisms sensence, how patterns of ageing evolve, how genes and environments drive then etc then a lot of this research is rooted in evolutionary theory with empirical studies spanning all kinds of organisms in the field and lab. So for this perspective a broader-based biological degree may be more appropriate.