I wanted to take a look at the competition, and the age they were when they were allowed to be in the starting halves on a consistent basis:
Brisbane Broncos: Adam Reynolds (33) - 22
Canberra Raiders: Jamal Fogarty (30) - 27
Canterbury-Bankstown Bulldogs: Kyle Flanagan (25) - 22
Cronulla Sharks: Nicho Hynes (27) - 26
The Dolphins: Sean O'Sullivan (25) - 23
Gold Coast Titans: Tanah Boyd (23) - 23
Manly Sea Eagles: Daly Cherry-Evans (34) - 22
Melbourne Storm: Jahrome Hughes (29) - 25
Newcastle Knights: Jackson Hastings (27) - 20
North Queensland Cowboys: Chad Townsend (32) - 24
Parramatta Eels: Mitchell Moses (29) - 21
Penrith Panthers: Nathan Cleary (26) - 19
St George Illawarra Dragons: Ben Hunt (33) - 23
South Sydney Rabbitohs: Lachlan Ilias (23) - 22
Sydney Roosters: Sam Walker (21) - 19
Warriors: Shaun Johnson (33) - 21
Wests Tigers: Luke Brooks (29) - 20
So the average age is 28, with players making that transition into halfback at around 22 years of age.
Let's take it back 20 years to 2003.
Brisbane Broncos: Shaun Berrigan (25) - 23
Canberra Raiders: Brad Drew (28) - 28
Canterbury-Bankstown Bulldogs: Brent Sherwin (25) - 22
Cronulla Sharks: Brett Kimmorley (27) - 22
Manly Sea Eagles: Jackson Ferris (27) - 20
Melbourne Storm: Matt Orford (25) - 22
Newcastle Knights: Andrew Johns (29) - 20
North Queensland Cowboys: Nathan Fien (24) - 21
Parramatta Eels: Paul Green (31) - 22
Penrith Panthers: Craig Gower (25) - 24
St George Illawarra Dragons: Brett Firman (21) - 21
South Sydney Rabbitohs: Willie Peters (24) - 19
Sydney Roosters: Brett Finch (22) - 20
Warriors: Stacey Jones (27) - 19
Wests Tigers: Lincoln Withers (22) - 21
So the average age was 25 with players making that transition earlier at 21. That figure could be lower depending on your definition of making that transition - Gower spent a fair time in the halves when he was 21 but switched back to dummy half until he was 24.
Similarly Brad Drew had a stint in the halves when he was 23, but was a dummy half until 2003 where he slotted in that position for Canberra.
There's a few factors in play here like advances in sports medicine, more clubs, smarter managers etc. However I'm more interested in what happened to the mid-20s halfbacks. Cleary is arguably the best player in the game and is on track to become one of the best halves in the history of the sport, but where is his competition?
Brodie Croft, Jake Clifford, Jack Cogger, Troy Dargan, Chanel Harris-Tavita, Brendan O'Hagan all had raps on them but they were all chewed up and spat out. Maybe they'll step up in the coming years, but their absence has definitely seen some players have prolonged careers in the NRL.
Looking at that 2003 list, you'd have to say less than half those clubs were satisfied with their #7. Bulldogs, Sharks, Storm, Knights, Panthers, Roosters & Warriors all stuck with their halves and even so there were some bumps in the road. It's a really difficult position to get right, but when clubs do they invariably achieve a lot of success.