Board Thread:Theories and Rumors/@comment-30938718-20180803102949/@comment-24889266-20190323204926

In terms of the actual villains themselves, here's my thoughts:

Samukai: He is undead and it is never revealed when he was originally alive as a human.

Pythor: Pythor is somewhere between 60-80 years old as he was an adult when the Serpentine were imprisoned 40 years prior to the events of the series. He is biologically younger because Serpentine appear to age differently than normal humans, as Pythor did not change physically between his imprisonment and him being freed by Lloyd.

Kozu: Kozu was created back when the First Spinjitzu Master was a young man so he is thousands of years old.

The Overlord: The Overlord is a dark entity that battled the First Spinjitzu Master during the early parts of Ninjago's history, making him thousands of years old.

Cryptor: He was built during the events of Rebooted so he is only a few days old. He is a Nindroid and they don't age.

Chen: Chen is older than Clouse and appears to be around 60-80 years old. He, however, has a daughter around the Ninja's age, and Chen's wife (the old Master of Amber) could possibly have been younger than him, however, she has never appeared.

Morro: Morro was a child when Garmadon left to train under Chen and was around the same age when he was refused the title of the Green Ninja. He left to find the FSM's burial site and he was around the Ninja's age when he perished in the Caves of Despair.

Nadakhan: He was around back when Soto's crew owned the Destiny's Bounty so he is around 200 years old.

Yang: Master Yang is undead, though it is believed that he originally became a ghost hundreds of years before the series.

Acronix & Krux: The time twins appear to be young adults in their 20s or 30s when their powers were absorbed into the Time Blades. Due to Acronix spending 40 years in a time vortex while Krux didn't, Krux is now biologically 40 years older than Acronix.

Harumi: Harumi was a child when the Great Devourer attacked Ninjago. She appears to be around the Ninja's age in the present day.

Iron Baron: He is possibly around 50, although he is most likely one of the older members of the Dragon Hunters.

The Omega: The Omega is one of the oldest villains. He has likely been around for thousands or even millions of years.