Functional Dependencies Present:
{Age, Sub_Enrolled} -> {Student}
{Student,Sub_Enrolled} -> {Age}
{Student} -> {Age}
{Age} -> {Student}
Here, total 2 candidate keys Are Present,
{Age, Sub_Enrolled}
{Student,Sub_Enrolled} .
All are Prime Attributes.
BCNF gets violated due to 3,4 F.D. mentioned above.
Answer : 3NF (It gets Satsfied.)