Previous evidence highlights the importance of alpha and gamma oscillations in large-scale functional networks for the selection and maintenance of relevant information. To investigate developmental changes of activity in both frequency bands in relationship to age related differences in behavioral performance, MEG activity was recorded in a sample of participants aged between 12 and 24 years while they performed a delayed match to sample WM-task. The findings of this research show that young adolescents have a reduced WM capacity as compared to adult participants. This reduction in WM capacity in young adolescents was also associated with markedly decreased behavioral performances in the presence of distractors and with developmental changes in alpha and gamma band activity. Importantly, developmental changes in rhythmic activity at alpha and gamma frequencies were found only in the distractor condition, further highlighting the importance of alpha and gamma oscillations during the inhibition of distractors and the selection of relevant information. The results from the present study confirm previous evidence showing that alpha and gamma oscillations differentially contribute to the maintenance of information WM and provide important evidence for a functional relationship between the development of WM capacity, distractor-inhibition and rhythmic activity in the alpha and gamma frequency bands.