The Junior Hockey pyramid in both USA and Canada is much larger than people seem aware.
All for 2024-25 to date
NAHL Weighted Average Age 19.667
BCHL Weighted Average Age 19.261
AJHL Weighted Average Age 19.193
QMJHL Weighted Average Age 18.848
USHL Weighted Average Age 18.824
OHL Weighted Average Age 18.733
WHL Weighted Average Age 18.687
and just comparison
NCAA Weighted Average Age 22.433
NAHL = no limits on number of 20 year olds that can play on a team
USHL and the 3 CHL leagues = Max of 20 year olds per game
NCDC = Max of 8 20 year old skaters per game
Also the EHL is the current leader in Division 3 NCAA commitments for what it's worth. That could shift to NAHL based on recent decision. EHLP often feeds into EHL.
The USPHL (which broke off from USA Hockey) is a league that moves players up quite a bit, often to NCDC, NAHL and Canadian Junior A. The USPHL-Premier is the top one of these two, and the USPHL-Elite often feeds into Premier.
In addition to the AJHL which is Canada's Best Junior A Hockey (with BCHL being an independent), there's the NOJHL, MJHL, SJHL, CCHL which are sending players to American and Canadian Universities presently.
The GOJHL is the one that functions most like a Minor League for the OHL. They were considering going independent, but may not with the recent decision as you may see more affiliations across all the Canadian Junior A Leagues.
NA3HL is the official third tier of the USA Hockey Pyramid but generally not as good as the independent ones mentioned above. A few NCAA D3 commits but mostly ACHA players from here, this one may not be around too much longer.