Tanay, most B.Sc Colleges have University level entrance examination which means the University will conduct admission to its courses specific to that University alone. It is not like other entrance examinations like NEET or JEE or CLAT where in one entrance exam score is recognised by many Institutions. And there are few Colleges also which conduct admissions based on the merit scored in your 12th. And for admission through both the modes, there is no upper age limit for joining B.Sc. If you feel overwhelmed going to regular college at the age of 29, you can also take up B.Sc through Distance learning. Post B.Sc Mathematics, You can either take up a Post Graduate degree in Mathematics or Statistics. You can also take up MBA because there is  no subject specification in MBA.