Mal has been sober since 1987. Alcoholism did run in his family, mostly in his uncles, who were great role models to him growing up. 

He first picked up a drink playing around with it here and there at the age of twelve/thirteen. It got serious when he was fifteen going to a school dance and he was going to meet girls, and he felt the need to feel comfortable, so he drank Southern Comfort and that worked wonders. This was a memory he remembered. It was a matter of fitting in and feeling good about himself. 

When his father died, he was only sixteen years of age. That's when the drinking escalated. There was no way of coping for him. He didn't have a lot of courage about him, so he felt he needed the alcohol. After that, it just progressed as time went by. At  the time it didn't ring any bells that the drinking was what was causing all of his problems. This realization came later on when he couldn't stop once he started. 

Mal should have died over and over again, but thankfully he lived to tell his story. Listen here.