"Thank God," he says, over a pasta lunch (he's a lifelong vegetarian) in a Santa Monica, Calif., restaurant. "In 'Rocky,' I'm playing 28, so that's unbelievable."
In "Bedford Diaries," created by Tom Fontana ("Oz," "Homicide: Life on the Street"), Ventimiglia plays Richard Thorne III, a former bad boy who edits his New York college newspaper and attends a human behavior and sexuality seminar taught by professor Jake Macklin (Matthew Modine). Playing his classmates are Tiffany Dupont, Penn Badgely, Corri English, Ernest Waddell and Victoria Cartagena.
In the 2007 feature film "Rocky Balboa," the sixth "Rocky" movie, again written and directed by its star, Sylvester Stallone, Ventimiglia plays Rocky Balboa Jr., son of the legendary Philadelphia boxer.
Ventimiglia has also signed on for an NBC pilot called "Heroes," about people who discover they have superpowers.
It may seem odd to do a pilot when one already has a series, except that The WB recently announced it was merging with UPN this fall to create a new network called (for the moment) The CW.
"I called Tom," Ventimiglia says, "and I'm like, 'So?' He's like, 'I've never been on a network that's been canceled.' We started laughing about it. Who knows? I mean, it could work out. Ten years into the business for me, I'm like, 'Cool,' if it doesn't, what are you going to do about it?"
Although Ventimiglia and Badgley play classmates in "Bedford," there's about a decade's difference in their ages, which worked out to the relief of Fontana.
"I was very concerned about Penn," Fontana said in a January interview. "If I was 18, if I had money from a TV show and looked like Penn Badgley, and I was in New York, I would go wild. I got very parental, which is not very much like me.
"But it was Milo who took him under his wing. ... Milo was like the great older brother."
"Penn's a bright guy," Ventimiglia says. "He didn't need me or anybody. There is that concern because he's 18 going on 19, but if you know Penn, he's not capable of putting himself in a position where he's going to get hurt, arrested or in trouble.
"The reason that Penn and I even discussed living together was saving money. When Tom got wind of it, he was like, 'Thank you so much for doing this.' The funny thing was, Tom was like, 'Julie [Martin, an executive producer] was so worried.' I'm like, 'Julie wasn't worried. You were worried.' He really deeply cares about everybody and the process."
Ventimiglia is equally impressed with Stallone after shooting "Rocky Balboa" with him in Los Angeles and Philadelphia.
"The first time I met him," he recalls, "he had a big smile on his face. He's physically twice me, just big. His hands are huge, and he's got that deep, booming voice that just engulfs you. It's very intimidating. But he's also just quiet at times and soft, just a normal guy.
"Of course, I respect the guy because he's done a lot of work; he's a talented writer."
The two even share a crooked lower lip, in both cases the result of nerve damage at birth.
"[During the first meeting] I started laughing," Ventimiglia recalls, "and he looks at me, then he leans over to the casting director and says, 'His lip even hooks down like mine does.' I'm like, 'That's way too close!'"
Everyone knows the iconic visual image of Rocky dancing on the steps of the Philadelphia Museum of Art, and that can overshadow the fact that Stallone wrote not only the "Rocky" movies, but several of his other films, and directed four of the "Rocky" movies.
"He's my director, and he's playing my father," Ventimiglia says. "There are so many odd lines of approaching the work. In that sense, Rocky's a little slow, and my character's a pretty bright kid, so he talks to him like an 8-year-old.
"When I saw him turn Rocky on ... Sylvester talks, very animated, really bright. Then when he gets into the character of Rocky, he goes" -- Ventimiglia lets his expression go slack -- "and then he starts looking around. He has this simple smile on his face, and he gets very slow. He does this before every take."
And it's not just Stallone's acting that impressed his young co-star. "When I read the script, I was impressed by it. I said, 'This is a really good story, even if it wasn't a 'Rocky' film. It's written well; it's funny; it's heartfelt.
"Then being on set with him, seeing how hard he works to get the shots cinematically. It's a beautiful, beautiful film. He did such a good job with it."
Ventimiglia also has ambitions behind the camera with his own production company. "We're going out with three TV projects this year," he says. "It's so much work. We just got this option on a book. It's one of those things where my partner and I were like, 'If we don't get it, don't have to work so hard.' Now we're like, 'Great.' Oh, my God, I'm going to go gray and bald in the next year, just working on this story as well as three other films and three other TV shows we have."
While Ventimiglia might appear in some of these projects, don't expect to see his girlfriend, "Gilmore" star Alexis Bledel.
"Separate church and state," Ventimiglia says. "It's just best to keep all that separate."