They don't really mention specific years that he was in the game for after arriving in America and becoming a boss in Miami distributing cocaine supplied by Alejandro Sosa.

So how many years was Tony in business for before he got shot dead in his mansion?

3? 5? What was it?

Nevermind, I found the answer. His career lasted only 3 years from the time he arrived in Miami.

Antonio "Tony" Montana was a Cuban-American drug lord who ruled Miami, Florida during the 1980s. Montana was one of the 25,000 Cuban criminals to arrive in the United States during the Mariel boatlift of May 1980, and he worked his way up the ranks of Miami's criminal underworld, working for Frank Lopez before taking over his organization for himself. Montana became a very wealthy man, but his marriage and empire collapsed due to his rash decisions caused by his cocaine addiction and his greed. In 1983, he betrayed his former ally, Alejandro Sosa.