Now that he’s no longer prohibited from being funny on television, Conan O’Brien attracted a sizable audience to his TBS debut on Monday night.

“Conan” scored a solid 4.2 million total viewers, as well as 3.3 million adults 18-49. The show also posted the youngest audience in talkville, attracting a median age of 30, according to Turner Research.

“Conan” took a bite out of Comedy Central’s “Daily Show” and “Colbert Report” and also bested his old home, NBC’s “The Tonight Show,” in all major measurements.

“The Tonight Show With Jay Leno” even wound up behind “Late Show With David Letterman” in adults 18-49 (1.3 million vs. 952,000).

Opening night does not signal much of anything — check back in a few weeks to see where “Conan’s” average aud settles. But it’s a strong enough start to leaveTBS very optimistic about its investment in the latenight host.

“Conan’s audience has been very vocal online, and he clearly made a smooth transition from Twitter to TBS,” said Steve Koonin, prexy of Turner Entertainment Networks. “Conan delivered an extraordinary audience and stands out as the youngest latenight talkshow on television.”

With such a large chunk of younger viewers, however, it’s unclear how much of that crowd — which doesn’t watch much talk in latenight (gravitating instead toward Adult Swim and other programs) — will stick around. But O’Brien has become a folk hero of sorts to younger viewers — and his status as a bit of a cable underdog may keep the host a favorite with that demo.

O’Brien also appeared more comfortable in his new digs, even bringing out the Masturbating Bear (a staple of NBC’s “Late Night” that was unseen for most of his brief “Tonight Show” run) on night one.

“The Tonight Show With Conan O’Brien” bowed last year with boffo ratings as well, averaging 6.1 million viewers in week one and a 2.3 rating with adults 18-49 — close to the number O’Brien pulled on his first night at TBS. But O’Brien’s “Tonight Show” eventually saw its numbers erode, and it began to battle CBS’ “Late Show” for demo supremacy.

Ironically, despite those ratings dips, Leno’s “Tonight Show” is currently drawing lower ratings than O’Brien’s edition did a year ago.

The heavily promoted and highly anticipated return of O’Brien bowed Monday with guests Seth Rogen, Lea Michele and Jack White — as well as cameos from Ricky Gervais and Larry King.

As for “Conan’s” new lead-out, “Lopez Tonight” averaged 1.4 million viewers — putting it ahead of the Comedy Central shows — and brought in 883,000 adults 18-49.

“Lopez” garnered the second-youngest latenight talker aud on Monday, posting a median age of 32.

The young cable audience — “Daily Show” and “Colbert” also bring in a median age under 40 — contrasted with that of the broadcast nets: Leno (median age: 59) and Letterman (53) bring in a substantially older aud.