Online discussion forums have been identified as an online social milieu that may facilitate the radicalization process, or the development of violent narratives for a minority of participants, notably youth. Yet, very little is known on the nature of the conversations youth have online, the emotions they convey, and whether or how the sentiments expressed in online narratives may change over time. Using Life Course Theory (LCT) and General Strain Theory (GST) as theoretical guidance, this article seeks to address the development of negative emotions in an online context, specifically whether certain turning points (such as entry into adulthood) are associated with a change in the nature of sentiments expressed online. A mixed methods approach is used, where the content of posts from a sample of 96 individuals participating in three online discussion forums focused on Islamic issues is analyzed quantitatively and qualitatively to assess the nature and evolution of negative emotions. The results show that 1) minors have a wider range of sentiments than adults, 2) adults are more negative overall when compared to minors, and 3) both groups tended to become more negative over time. However, the most negative users of the sample did not show as much change as the others, remaining consistent in their narratives from the beginning to the end of the study period.