Introduction: Brain processing of odorants in different stages during adolescence is not well understood. This study aimed to investigate differences in brain processing of pleasant and unpleasant odors between adolescent girls at different ages. Methods: Eleven girls aged 9–10 years and 20 girls aged 15–16 years participated in an fMRI study (1.5 T, repetition time 2.5 s) where two odorants (peach and n-butanol) were delivered passively to the participants’ nostrils. Psychophysical measurements for odor intensity, pleasantness, and familiarity were recorded. Results: Compared to older ones, younger girls were less familiar with peach odor. Stronger brain activation of piriform cortex, amygdala, bilateral insular cortex, anterior cingulate cortex, and dorsal striatum (caudate and putamen) was observed in younger vs. older girls, whereas in older girls there was no superior activation in olfactory regions as compared to younger participants. Conclusion and Implication: The findings demonstrating differences of brain activation patterns between girls of two age groups may reflect olfactory perception development during adolescence.