Short story:

Phase 1. Ratings, 2-3 years.
Phase 2. CFI 2-3 years to 1500tt
Phase 3. Commuter/regional 2-5 years.
Phase 4. Career job. So 6 to 11 years to career job.

Long story:

Your friend will need his ratings. Assuming he has none right now that will take about 2 years at a local fbo (pvt,inst,comm,cfi,commel). You indicated he already has a career, good, he works and flies. Nothing else (unless he has a family). That's phase 1.

Phase 2, now he can get paid to build time. Most likely it will be CFIing (or banner, pipe, traffic ect.) with a spattering of right seat charter tossed in. This will be about 2-3 years from 250tt to 1500tt which drops us off at phase 3.

Phase 3, commuter/regional airline time. Assuming the current hiring environment stays the same:

He applies, interviews and fogs a mirror, gets hired and makes it thru training. Now he's climbs the seniority ladder, upgrades, checkairman and applies or flows to a major or hired by an LCC or makes his career at the regional/commuter.

Phase 4. Career job. Whatever floats his boat. Senior at a commuter/regional - fine, LCC - fine, cargo-fine, legacy - fine, charter (125 or 135) or part 91 corp - fine. You get the point.

Depending on how hard he hits it and how lucky he is, it will be between 6 to 10 years to phase 4.

Good luck. Jumping the hoops hasn't changed much, except that there is no or very little 135 cargo time anymore. 15 plus years ago this was a step between phase 2 and phase 3 that lasted about 1 or 2 years depending on the commuter hiring environment. How most of us cut our teeth before going to a commuter prior to the early 2000's. Now it's cfi until 1500tt.

Of course if his last name is Hilton or Kennedy and he can poop cash or he doesn't mind going into debt then he can shorten some of the phases listed above by going to a puppy mill school.