Manny Pacquiao smiled at the question, as many boxers before him have, flexed his right biceps and grinned in delight.

"I still feel young and strong," Pacquiao proclaimed last week.

Birthday No. 33 comes for Pacquiao on Dec. 17.

Floyd Mayweather Jr., the man the boxing world wants Pacquiao to fight if Mayweather withstands the challenge of 24-year-old Victor Ortiz on Saturday in Las Vegas, will turn 35 on Feb. 24.

"One lesson we've learned in this sport is that day arrives for fighters when they wake up and find out something they believed was written in stone as unchanging has changed," HBO boxing analyst Larry Merchant said.

Time stops for no man, and the calendar's toll can be severe for a boxer.

"My father — my greatest educator — told me since I was a little boy that at 28 you're still a young man, but you're an old fighter," said Ray "Boom Boom" Mancini, the former world lightweight champion. "Years later, I heard a quote by Napoleon: 'After 30 years, a man's spirit is not made for war.'"

Mancini, now 50, fought twice after turning 28 and lost both times.

"Your body starts to shut down, you start settling down," Mancini said. "We change mentally, emotionally, physically. The piss-and-vinegar attitude goes away. The reflexes aren't the same. In training camp, you do seven reps instead of 10 and think, 'Don't worry about it.' But you're not pushing yourself the same, and you pay for it."

Oscar De La Hoya experienced that deterioration three years ago against Pacquiao.

De La Hoya couldn't move fast enough to keep up with Pacquiao's attacks, and he couldn't hit the bolting Filipino. By the ninth round, De La Hoya, then 35, quit on his stool and ended his proud career.

Now retired, De La Hoya admits he'd begun slipping years earlier and was "past his prime" when he lost to Mayweather by split decision in 2007.

"It's a whole new ballgame, and Floyd's going to find that out now that he's 34," De La Hoya said. "Things start happening at 34. Your muscle mass is not the same. You make weight easier, but that's not a good thing because you have less muscle.

"I thought of that when I saw Floyd's number at his 30-day weigh-in: 149 (for the Ortiz bout, while normally a fighter would be up around 155 at that time). It's not a good sign for Floyd. Everything is against him."

Longtime boxing publicist Bill Caplan was an eyewitness to the toll of age on Sugar Ray Robinson. He watched Robinson, at 39, struggle in two bouts against Gene Fullmer, and then in training camp before Robinson's sad loss to part-time bartender Ferd Hernandez in 1965 in Las Vegas.

"They don't lose their power, they lose their timing," said Caplan, who has since worked with De La Hoya, George Foreman and now Ortiz. "If they see an opening, they can't pull the trigger.

"You also can't spar as many rounds. The body just can't take it. So when you get in the ring in that condition, you look terrible."

There are exceptions.

Former world heavyweight champion Foreman returned from a 10-year hiatus at age 38, then recaptured the belt at 45. He preached that "age doesn't matter ... you lose energy, but gain wisdom."

Light-heavyweight champion Bernard Hopkins, 46, will defend his belt Oct. 15 in Los Angeles. Hopkins said his secret was a vow in his 20s to remain true to a strict diet and exercise regimen.