Marksmen rarely, if ever, hit even 20% CDR, unless they specifically opt into Lethality or Essence Reaver. Most often, you see 0%. The only meta way for them to cap is Essence Reaver (with a Zeal item, of course, but that's a given) and Death's Dance.
Enchanters regularly hit 55%, given how much goddamned CDR they have in everything. There's just no way to escape it as a real enchanter.
Tanks can hit between 10 and 50%, depending on who they are, and what they need at the time.
Juggernauts hit about 40%. Sometimes 50%. Although I've seen them at only 20%.
Mages generally hit about 35%. 45% on the dot if they pick up both Banshee's and Zhonya's, on top or Morello.
Tank supports had 10-20%, last time I checked. But that could have gone up quite a bit recently.
Bruisers tend to have quite a bit. 30% is common.
Assassins have a largely varying amount. 30-45% is possible for an AD assassin, while you can have a meager 10-25% on an AP assassin.
Skirmishers have...quite a big variance. Someone like Yasuo gets none, while Riven opts into a solid 30-40%.
Mages honestly don't cap any more or less often than the average. They're actually the average. 35%.