table1: student
attributes: name , roll, dob
primary key: roll


table2: info
attributes : name , age;
foreign key : name(student)

I want to enter values in student table and info table would automatically
update through student table.
is it possible. if yes, then how ?

Depending on what you really want to do, you may be able to do this using a trigger. . .

What do you want automatically updated?

the second table is redundant as you have their name in the first table and age can be calculated from the dob in the first table.

Do you want the current age (runtime) or the age when the data was inserted?

And yes, it is best to NOT store data that can be derived at run-time (i.e. fixed data like the difference between to stored dates).