From a young age, Tywin was disinterested in learning. He was most successful in the training yard. Swordfighting came easy to him, and he quickly became a warrior of great prowess. By age 16, Tywin set off as a hedge knight in hopes of finding glory, fighting in tournaments across the realm.
His life of adventure came to an end with the onset of the Second Greyjoy Rebellion. Tywin returned to the Westerlands to fight for his liege, Lord Tyrius Lannister, participating in the Battle for Lannisport and earning prestige for his contributions and those of his house. After Tyrius' death on Pyke, Tywin fought under the new Lord Loren Lannister’s host until the Greyjoys surrendered.
Due to his skill at arms and contributions during the war, Tywin was invited to be Matser-at-Arms of Casterly Rock, where he trained both Damon Lannister and Thaddius Lannister after their return from Pyke.
When the Lannisters seized the throne, Tywin was invited to join the Kingsguard under Damon, fighting by his side at Stonehelm and the Kingswood.
Tywin continued to serve the Lannister King, leading troops in the Riverlands. After the coronation of Queen Danae Targaryen, he became her guard and developed a father-like bond with the young ruler.
When Danae fled the capital for Dragonstone, Tywin was ordered to go after her and beg her return. After finding the port of Dragonstone closed and spotting the dragon Persion flying above the volcanic island, the captain of Tywin's ship refused to go any further and turned back for the capital. A storm overtook them during their passage and the ship was wrecked, leaving many to presume that Tywin was deceased.
Tywin was nursed back to health by a women named Sasha, who found him washed up on the coast near Rook's Rest. The two developed a relationship and Tywin was tempted by this new, simpler life. However, unwilling to break his vows, he returned to King's Landing to serve the King and Queen.
"Lannister crony." - thoughts of Ser Varus