I believe it's genetic and the study below shows the risk increases greatly for those that start smoking. Here's a study done with the involvement of 3 countries compiling 40 yrs of data:
Genetic Factors Linked to Smoking Addiction in Teens - Forbes
And another study:
A genetic association for cigarette smoking b... [Health Psychol. 1999] - PubMed - NCBI
Genetic Factors Linked to Smoking Addiction in Teens - Forbes
And another study:
A genetic association for cigarette smoking b... [Health Psychol. 1999] - PubMed - NCBI