"I think if we can just not get hurt, I think the ballclub is going to do well," Aaron said.
Letterman then asked Aaron about how the game has changed since the time in which Aaron played (1954-76), and Aaron didn't hesitate to mention the current game's, well, hesitation.
"I think the thing that troubles me most is the length of the game," Aaron said. "I would like to see the game shortened a little bit more. And I don't know how we can do it, but in the seventh, eighth or ninth inning, you may see three or four different ... pitchers go out and pitch to one batter.
"In some way, we've just got to shorten the game up a bit."
Letterman's comic timing shined through on his response, sparking heavy laughs from Aaron.
The host agreed with Aaron's assessment and added, "You could leave in the third inning, go out and look for an apartment, come back and the game is still going on!"
Aaron riffed on that, remembering when aces Sandy Koufax and Bob Gibson would pitch complete games that seemed to last only "an hour."
"I tell a lot of people that it's a funny thing about those two pitchers and maybe a few more, is that when they get in the seventh, eighth or ninth inning, you can call your wife or girlfriend and say, 'Put the supper on, because I'll be home in a couple of minutes,'" Aaron said. "You can't do that now."
The mere mention of the intimidating mound presence known as Gibson got Letterman to ask Aaron just how tough the Cardinals pitcher was, and Aaron said with a straight face that Gibson "would even knock you down in the on-deck circle."
That got Letterman and the crowd in the Ed Sullivan Theater laughing, as did Aaron's tale about striking out three times in a game against Sam Jones early in his career.
"That was the worst," Aaron said. "That was the most embarrassing thing in the world. ... I [took Jones] out to dinner that night and looked him in the face and told him you'll never have that opportunity again. And I meant it. And from that day on, he and I had an understanding."
Letterman asked Aaron if any pitchers threw 100 mph back when he was playing, and Aaron said he thought Koufax probably got close, although it wasn't the speed of the pitch that was so tricky; it was how "light" or "heavy" the ball seemed based on movement.
"A ball thrown hard does not bother you," Aaron said. "And if you get hit, it only hurts for a little while."
Letterman marveled at the fact that Aaron hit as many homers as he did while fluctuating between 170 and 180 pounds for a good deal of his career, prompting Aaron to drop the line of the night.
"Making the kind of money I was making," Aaron said of his light weight, "it was probably from malnutrition."
Letterman then brought out old photos of Aaron -- one from when he was 19 years old and one of him at an All-Star Game next to Willie Mays. Aaron appeared in 25 Midsummer Classics, and Mays played in 26.
"Willie and I got to be very good friends my first year in the big leagues after he came back from the Army," Aaron said. "He is truly one of the greatest players to ever put on a uniform."
And being in New York, Letterman asked Aaron the requisite question of what he thought of Mickey Mantle's abilities.
"I knew Mickey very well," Aaron said. "Too bad he played the last few years with his bum leg. Mickey, when he first came up, probably had more ability than any of us. From running, power and just pure talent, I think Mickey had everything."
But Aaron was the first to break Babe Ruth's Major League home run record of 714, and Letterman asked him about that night in 1974, when he was greeted at home plate by his mother.
"God bless her," Aaron said. "She got to home plate before I got to first base. ... She was so happy. I was excited about her being there."
Aaron was also excited to donate the $14,000 he won on the old Home Run Derby TV show to his father to buy a family grocery store.
Letterman reminisced about enjoying that show as a kid, which conjured up more memories for Aaron.
"Being in Milwaukee, I knew that they were only going to give me one chance," Aaron said. "They were going to ... call back Mickey Mantle twice, they would call Willie Mays back twice. And I said [to myself], 'Henry, you being from Milwaukee, you'll only get one chance, and you'd better be ready. And I was ready."
Aaron was appearing on the show to promote Topps, the famous baseball card company that is celebrating its 60th anniversary.
Part of the Topps celebration includes special editions of the cards that feature autographs by legends of the game. Aaron signed cards for three editions -- Topps Heritage, Topps Tribute and Gypsy Queen -- as did Koufax.
And in the spirit of this "diamond" anniversary, Aaron, the living icon of the diamond, presented Letterman with a Topps David Letterman card that had a real diamond stitched into it.
Letterman was visibly touched, although he managed to find some humor in the photo on the card, which showed the tall gray-haired right-hander releasing what very well could have been an awkwardly pitched ball.
"Forgive me for saying this," the television fixture said to the baseball hero, "but I throw like a girl."