I'm sure you've probably heard of the most well-known event in Lenin's early years that steered him towards revolutionary activity - the execution of his brother, Aleksander Ilich Ulianov, for attempting to assassinate the Tsar.
This took place in 1887, when Aleksander was 21 and the young Lenin (then Vladimir Ilich Ulianov) only 17 years old. Of course, the execution of his elder brother for taking part in a populist-inspired plot to kill the Tsar can definitely be read as the spark for Lenin's political radicalization. However, one must be careful to not put too much weight on this single event. Soviet histories & hagiographies of Lenin often narrated this as the pivotal moment in the bildungsroman of the heroic revolutionary - claiming that Aleksandr had studied politics & political economy with his younger brother, and even first introduced him to Marx while home in Simbirsk from university.
The culmination of this myth is the story that, on learning of his brother's arrest and execution, the 17-year-old Lenin exclaimed "We will go down a different path (Мы пойдем другим путем)". Immortalized in this famous socialist realist painting, the basic idea is that the young Lenin had already realized (in 1887) that the strategy of individual terrorism pursued by the populists, his brother, and later the SRs was doomed to fail, and that only a Marxist revolutionary movement could steer Russia down the correct path.
This is, of course, an absolute myth - far from already espying the true path of revolution, the young Lenin knew nothing of his brother's political leanings until his arrest, and himself was apolitical as a young teenager. However, at the same time we cannot discount the impact that this family trauma must have had on the bright Vladimir Ilich - as was the case for many Russians from the 1840's onwards, the Tsarist autocracy's brutal repression of friends and relatives served to only further radicalize the student youth and create new generations of revolutionaries.
For a work that covers both this incident from Lenin's youth as well as its later Soviet mythology, see:
