This could probably warrant a research project on its own, but I will ask here in case anyone is knowledgeable about this.
There are multiple studies that show that choosing age or even race appropriate templates can affect normalization and segmentation results. In response, many groups published age-specific MRI templates.
However, even very recently, countless published youth functional connectivity studies just use the MNI templates. Some that use in-house templates still do not distinguish young adults and pre-adolescents. Only studies on infants and very young children make sure to use age-specific templates.
Perhaps due to the nature of how ROI functional connectivity measures are calculated, the choice of template does not matter too much? Or is this a widespread bad practice in the field? I could find no prior research on how choice of template affects functional connectivity specifically.