I've reached 1284 A.D. but still can't build or recruit any gun powder units.

[Nata Aquinta]

I'm playing Late Era Campaign and "A New Deadly Weapon" era has come, but they are still unavailable. I can't build any canon workshop or alchemist academy and other building of gun powder age. What's wrong with it?

[Duck of Death]

Its possible you don't have some prerequisite buildings constructed yet, or that you don't have high enough level cities/castles.

However, the canon/alchemist buildings don't always show up immediately. Sometimes it takes a few turns for some reason.
Also, even after you've constructed alchemy and canon buildings, canons aren't always immediately available to recruit... but they will be shortly after.

Keep in mind that though gunpowder and canons were a concept in 1284, they didn't really start to become used in significant numbers until 150-200 years later in ground warfare (particularly in the west).
Youll probably see canons available on ships before you see them for land, since they were initially large, heavy unwieldy things that were more of a bother in ground warfare then a bonus.

[FunkMasterAnus]

Don't worry about it. It mainly depends on the faction you're playing, because my favorite faction (Byzantines) doesn't get gunpowder units for a long while. I'm pretty sure only Venice and Genoa get gunpowder right at the event, as other factions need to wait till like the early 1300's to get cannons first, then get actual gunpowder infantry later. The reason I mention Venice and Genoa is because they get a unit called "Handgunners" that legit use a hallowed-out pole and shove gunpowder and rocks in it, so they aren't very good, but they get them after that event.

[Nata Aquinta]

Yeah, I see. Thank you both. Now I'm playing at late 1300 and I'm so tired for waiting for my favortite unit, musketeer.

[Roma_Victrix]

Yeah, I see. Thank you both. Now I'm playing at late 1300 and I'm so tired for waiting for my favortite unit, musketeer.

You're going to get the 15th-century medieval-style Arquebusiers (c. 1420, they look similar to Halberd or Pike Militia) long before the Musketeers. The Late Arquebusiers don't even show up until about 1500.