Up until about a year ago, Michael Rogers had lunch or cocktails a couple of times a week with the CEO of the New York public-relations firm where he worked. They’d split a plate of french fries or a carafe of sake and his boss would give him advice about how to be a better manager. Rogers, 30, had started at the firm as an account supervisor a couple of years earlier and had since been promoted to senior vice president.

“He was great about helping and guiding me,” Rogers says of the CEO. “He kind of groomed me to take over.”

Soon, though, Rogers had the itch to abandon his role as protégé and seek new challenges. Unsure of how to break up with the man who’d recently toasted him after they signed a new client together, Rogers went with a white lie. He told his boss he was overworked and stressed out and wanted to head to Los Angeles to regroup. The CEO hugged him and wished him luck.

About a month later, after he announced the opening of his own firm, Rogers got an e-mail from his old boss’s assistant. It was a succinct message reminding him that he’d signed a non-compete clause and the firm would file a lawsuit against him if he poached any of its clients or staff.

“I think he saw that I could succeed without him and that upset him,” Rogers says. “I was now a peer, no longer under his control or guidance.”

Even if one guy didn’t promote you up the ladder from intern to executive, you likely have someone in your professional life who’s taught you a few invaluable lessons—an avuncular older colleague with whom you have a strong rapport. Inevitably, there will come a point when in order to move forward in your career you will have to distance yourself from that person. And now that intra-office relationships are so much less formal, that extrication process is a lot more difficult.

“The biggest mistake people make is making things personal instead of professional,” says Steve Chandler, author of The Hands-off Manager: How to Mentor People and Allow Them to Be Successful. “If you have a golf coach and that person doesn’t have much more to teach you, it’s not a personal thing. You get a new coach. In the workplace, it’s more like ‘This is my new father.’ That’s how personal we make it.”

Complicating matters further, the natural life cycle of the boss-protégé relationship has been disrupted by the fact that office father figures are sticking around longer than ever. Almost half of the 2,000 senior-level managers at global companies—recently surveyed by Korn/Ferry—said they planned to keep working past the age of 64, leaving few shoes for up-and-comers to fill.

It’s hard to usurp the old guard in the legal profession as well. According to Vault.com’s 2006 survey of 19,000 attorneys, in 1998, associates made partner in an average of seven years. Today, it takes nine and a half years. “The reason is simple,” Vault.com copresident Sam Hamadeh told Fortune. “Partners aren’t retiring.”