T.J. Watt Can Catch My Sack Record

Could T.J. Watt one day be the NFL's all-time leader in sacks???

Bruce Smith -- the current sack record-holder -- certainly thinks so ... telling TMZ Sports the Pittsburgh Steelers star is "the one we want to watch now because he's young."

Smith has held the all-time sacks mark since 2003, when he logged his 200th career QB takedown ... and nobody has come close to the number since.

Guys like J.J. Watt and Von Miller -- two of the best of this generation -- barely have over 100, and their careers are winding down.

So, we had to ask ... does Smith think anybody will be able to get to his mark eventually??

Smith says it's certainly possible -- telling us the rules of the game will change enough…