Oscar De La Hoya -- I Would Fight Mayweather ... If I Was 5 Years Younger

Oscar De La Hoya says his strongly worded attack on Floyd Mayweather is NOT a publicity stunt to get Floyd in the ring ... saying he's NOT planning on a rematch because he's too old.

De La Hoya appeared on "TMZ Sports" on FS1 on Tuesday -- and we asked if he's afraid of meeting Floyd in the streets after blasting the guy as boring and saying boxing is better off without him.

The Golden Boy says he WOULD be down to scrap with Floyd ... if there was a way to turn back the clock -- but says for all intents and purposes, his fighting days are over.

We also asked Oscar about his $100,000 bet with Jay Z over the Canelo Alvarez vs. Miguel Cotto fight this weekend ... and De La Hoya made it clear, he wants Hova's money bad ... for a really good cause.