Fun Fantasy series with immense worldbuilding and great characters?

Wheel of Time doesn't really fit "recent," but still fantastic.

Way of Kings is great. Codex Alera is a fun read as well

Stormlight archives fits everything except protagonist. It has multiple protagonists, not just one. Some of the protagonists are indeed male and around that age.

Cradle series, by Will Wight. Fast paced, fun. Started on book one and could not stop myself from reading all the way to the end!

Classics:

• Amber series by Roger Zelazny
• Discworld series by Terry Pratchett

I think it really depends on what you mean by "fun", and how willing to stretch the 18yo male protagonist.

If fun just means on your toes excitement and generally being a good read, I can definitely second Wheel of Time. It's an older book, but reads like modern fantasy. Lightbringer is also a good one, though I haven't read the entire series.

If fun means more lighthearted or a positive outlook, that's not quite my expertise, but I have heard many good things about Discworld from many different people.

If you want to loosen the 18yo protagonist, lightning round! (There's a lot of Sanderson, but I do love his stories) Mistborn, by Sanderson: 18yo(ish) female protagonist, not your typical YA young girl though Stormlight Archive, by Sanderson: Multiple POVs, two maim ones being 18yo male and female. Great story, as others recommend. Kings of the Wyld, by Nicholas Eames: Follows an older protagonist, more of a mature tone, but it kept me hooked until the end.

I also have some scifi recommendations if you want those.

As others have said, the Stormlight Archive by Brandon Sanderson is a great one (has other main characters though) as well as the Kingkiller Chronicle by Patrick Rothfuss. It’s also encourage branching out past the male 18 year old main character though! The Broken Earth Trilogy by NK Jemisin is one of my favorite series and one of the better written I’ve read as well

Name of the wind fits that perfectly.

People need to stop recommending Pat Rothfuss. His stuff is awesome but he'll never be done it and as such were just adding more people to this waiting room of misery. Books that are equally excellent AND the author delivers:

• The First Law Trilogy
• Stormlight Archives
• Codex Alera
• Assassins Apprentice
• Red Rising (not fantasy but an amazing SciFi)

First Law and Red Rising are my top favourites!

I enjoyed the lightbringer series by Brent Weeks which matches your criteria.

My 3 main recommendations were already mentioned but I'll mention them again for visibility.

Stormlight Archives by Brandon Sanderson. There are actually multiple main characters, but the world building is top notch. I haven't finished the series yet (it's my "read during lunch" series atm) but so far there are 2 male main characters in the 18-25ish range

The Codex Alera by Jim Butcher. The main character starts around 12 and there are arguably multiple main characters, but it's a damn good series. Think ancient Rome but everyone controls elementals

Lightbringer by Brent Weeks. A fantastic series where the government and religions of the world are built around the magic system. The series happens over a few years but the main character starts at around 15

Since I mentioned Lightbringer I also want to mention The Night Angel Trilogy by Brent Weeks. It's a dark fantasy series featuring magically gifted assassins. Most of the good guys are criminals and murderers. It's a brutal series with an excellent cast of characters and a world that feels like it's been through hell. The main character starts off as a kid, but is in his 20s by the end of the series

Prydain is pretty good fare (you might remember The Black Cauldron), it's a strange mix of young adult and epic at the same time. Your protagonist doesn't start out as 18, it's a bit of a bildugnsroman, but he ends up thereabouts.

Robin Hobb's Farseer books fit, though Fitz is different ages throughout the story. Excellent series!

Hm. I just read Witch King by Martha Wells. New release with a sort of ~18 yo male protagonist. I'd recommend it on the basis of nteresting worldbuilding and characters. The plot is a bit softer and internal -like Goblin Emperor by K Addison.

If you want something a little darker anything by Joe Abercrombie

Red Rising series by Pierce Brown. It’s like stratified human civilisation / Roman Empire in Space. First book is very Hunger Games-y but the rest of the series is excellent.

Others have mentioned these, no doubt. But I think they’re worth mentioning again. Sanderson’s Cosmere material is a superb starting point to get into fantasy.

Mistborn era 1 is a tight, fast paced trilogy with fantastic world building and fun, loveable characters. The setting of these books, just the world itself, is one of my favorites for sure.

Stormlight Archive is an enormous fantasy series, essentially Sanderon’s magnum opus. He’s halfway through writing his fifth book in the series out of a planned 10 and it is so so fun. There are some older protagonists in this book, but they are all fantastic.

Third, not Sanderson (except the last three, sort of) is Wheel of Time. I started reading fantasy with WoT, because a 14 book series just sounded like a really fun adventure to go on. I was hooked after book one. It’s a huge series that follows a fairly small cast of main characters who undergo so much growth. The three core characters are all 18 year old males, give or take a couple years. It has what might forever be my favorite ending to a series. Maybe not though. I haven’t read a ton of fantasy yet.

Give any of those three a spin and I think you’ll find that you really like fantasy.