Drawing from Life Course Theory (LCT) and General Strain Theory (GST), the current study sought to address the development of negative affect in the online context, specifically whether the turning point of entrance into adulthood was associated with a change in the sentiment expressed online. A mixed-methods approach was employed, whereby 96 individuals were sampled from 3 online Islamic forums, and approximately 3000 posts per user were analyzed over 9 years. Quantitative results display a development in sentiment over time (increasing in negativity) for both minors and adults. Qualitatively, most users displayed a change in overall posting content throughout their time online; but a select few did not display any development – these individuals were the most negative/extreme on the forum. Implications of these findings for research on the role of the Internet in the development of negative narratives and extremism are discussed, as well as avenues for future research.