Hi there. 

First of all, no matter which college or University you choose in the world you can't become a doctor right away after 12. 

After passing Class XII, one has to study for 5 years with 6 months of compulsory internship to get the degree of MBBS. 

Getting into any medical college in India is not easy. One has to crack the NEET examinations in order to seek admission in a medical Institution. 

AFMC follows that same rule. And AFMC is only college in India that trains medical undergrads to become Army Doctors. 

There's no other way. 

Hope this helps. 

Wishing you luck!