A Jedi Master may not have more than one Padawan. This particular rule developed after the Old Sith Wars, as most ancient Masters such as Arca Jeth, Thon, Vodo-Siosk Baas and Krynda Draay did not have to abide by it.
The idea is that training someone up to being a fully-capable and independent Jedi is not something that can be done part-time, the Padawan needs the Master's undivided attention in that respect. Yoda did train many Padawans, but never more than one at a time as far as we know.
Padawans often train for at least a decade under a Jedi Knight or Master, and each Jedi can only take one Padawan at a time with few exceptions. Padawans must complete their Jedi Trials to ascend to Knighthood, which typically occurs in their mid-20s.
Overall, every Jedi was duty-bound to observe the tenets of the Jedi Code, one of which forbade the Jedi from training more than one apprentice at any given time. As Jedi, they were taught to resist temptations to the dark side of the Force, and as such they were trained to rely only on the light side for power.
According to Star Wars: Absolutely Everything You Need To Know, Yoda trained approximately 20,000 Jedi after reaching the rank of Master. Although it's a very impressive number, it's important to keep in mind that Yoda lived for 900 years, and became Master around the age of 100.
Over a century later, Yoda took on the human Dooku as his last known Padawan in the era of the Galactic Republic. In 90 BBY, Yoda undertook a visit to Serenno with other Jedi Masters and younglings Sifo Dyas, and Dooku.
Ahsoka Tano, a Togruta female, was the Padawan learner to Anakin Skywalker and a hero of the Clone Wars. Alongside Anakin, she grew from headstrong student into a mature leader.
Sidious broke the Rule of Two at least twice: once by training Darth Maul while still under the tutelage of Darth Plagueis; and secondly, by taking on two apprentices at once, and in the form of two Jedi: Count Dooku, the former Padawan of the legendary Jedi Master Yoda, dubbed Darth Tyranus, and the Fosh Jedi Vergere.
Although the 2002 film Star Wars: Episode II Attack of the Clones established that the Jedi Order members couldn't marry or have children, Star Wars creator George Lucas explained that despite their monastic regime, the Jedi were permitted to have sexual intercourse as long they didn't form attachments.
Arguably, some of the rarest types of Jedi were the so-called Iron Knights. These are members of the Shards species - crystals with a brain of their own. They were Force-sensitive and all trained under the tutelage of Jedi Master Aqinos. The Shards had droid bodies, similar to that of General Grievous.
As a mentor, Kenobi was responsible for training two members of the Skywalker family, Anakin and Luke Skywalker, both of whom served in turn as his Padawan in the ways of the Force.
She eventually became the Padawan of a human male Jedi Master, Stellan Gios. Vernestra was enough of a prodigy that she eventually attained the rank of Jedi Knight at the age of only fifteen, making her the youngest Knight in a generation.
A Padawan was typically a young adult at the time of their trial, although some prodigies like Vernestra Rwoh of the High Republic were as young as 15 years old. Some trials were completed through experience in the field; Obi-Wan Kenobi attained the rank of Jedi Knight in this manner.
Billaba became Windu's Padawan and trained under the Jedi Master in the ways of the Force. During her training, Windu allowed her to study Form VII variant known as Vaapad. She eventually became a Jedi Knight, renowned for her skills with a lightsaber and favored Form III when teaching other Jedi.
Did Mace Windu have a Padawan? Yes, Depa Billaba. In canon and Legends, she was Mace's padawan, and he even taught her Vaapad. She was a skilled Jedi Master.
Xanatos was a Force-sensitive Human male failed Jedi and the second Padawan of Qui-Gon Jinn, who earlier had trained a young Jedi named Feemor.
Jedi were forbidden from taking a political appointment. They were taught that their loyalty was to be to the Force, the Jedi Order, the Republic and to themselves, in that order. Nor they allowed to accept gifts - the latter did not include the traditional Padawan gift, given to the students by their Masters.
This is the most well-known of the Jedi rules. Love leads to attachment and attachment leads to strong emotions, which are the path to the Dark Side of the Force. Because of this, Jedi are forbidden to fall in love. This, of course, doesn't stop Anakin Skywalker from falling in love with Padmé.
In the Jedi Order, emotional attachment and possession were forbidden because it was believed they could lead to jealousy and fear of loss, and ultimately the dark side of the Force; for that reason, Jedi were not allowed to marry.
The Sith remained hidden for a millennium, allowing the Jedi to believe that their ancient nemesis had gone extinct. The Sith stayed in hiding for a thousand years, their survival unknown to the Jedi, as they continued their revenge against the Jedi through Bane's Grand Plan.
Anakin then pledges himself to the dark side as Palpatine's Sith apprentice, Darth Vader. Palpatine issues Order 66, commanding the clone troopers to turn on their Jedi generals, while dispatching Vader to kill everyone inside the Jedi Temple and then murder the Separatist leaders on the planet Mustafar.
He fell under the influence of Supreme Chancellor Palpatine of Naboo, and left the Jedi Order. After learning that Palpatine was secretly the Sith Lord Darth Sidious, Dooku turned to the dark side and became a Dark Lord of the Sith himself, replacing Darth Maul as Sidious's second apprentice.
After Obi-Wan Kenobi's capture on Geonosis, Dooku visited the younger Jedi – whose master, Qui-Gon Jinn, had been Dooku's Padawan. Dooku told Obi-Wan the Republic was under the control of a Sith Lord named Darth Sidious.
When Ahsoka was arrested for the bombing of the Jedi Temple and for killing clones and Letta Turmond, she was held at the Jedi Temple. Admiral Tarkin contacted the Jedi Council and relayed the wished of the Senate — that Tano be expelled from the Jedi Order so that she could be tried by a military court.
The Separatist Crisis and the Clone Wars were masterminded by Sidious and his new apprentice, Darth Tyranus, in an effort to achieve galactic dominance. Following an attempt to arrest the chancellor, the Great Jedi Purge commenced with Sidious enacting Order 66.