You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Genghis_Khan

Context:
Genghis Khan was aware of the friction between his sons (particularly between Chagatai and Jochi) and worried of possible conflict between them if he died. He therefore decided to divide his empire among his sons and make all of them Khan in their own right, while appointing one of his sons as his successor. Chagatai was considered unstable due to his temper and rash behavior, because of statements he made that he would not follow Jochi if he were to become his father's successor. Tolui, Genghis Khan's youngest son, was not to be his successor because he was the youngest and in the Mongol culture, youngest sons were not given much responsibility due to their age. If Jochi were to become successor, it was likely that Chagatai would engage in warfare with him and collapse the empire. Therefore, Genghis Khan decided to give the throne to Ögedei. Ögedei was seen by Genghis Khan as dependable in character and relatively stable and down to earth and would be a neutral candidate and might defuse the situation between his brothers.

Question:
Which's of Genghis Khan's successors could not be successor because of his age?

Tolui