In our HST photometric survey , we have been searching for multiple stellar populations ( MPs ) in Magellanic Clouds ( MCs ) massive star clusters which span a significant range of ages ( \sim 1.5 - 11 Gyr ) .
In the previous papers of the series , we have shown that the age of the cluster represents one of the key factors in shaping the origin of the chemical anomalies .
Here we present the analysis of four additional clusters in the MCs , namely Lindsay 38 , Lindsay 113 , NGC 2121 and NGC 2155 , for which we recently obtained new UV HST observations .
These clusters are more massive than \sim 10 ^ { 4 } M _ { \odot } and have ages between \sim 2.5 - 6 Gyr , i.e .
located in a previously unexplored region of the cluster age/mass diagram .
We found chemical anomalies , in the form of N spreads , in three out of four clusters in the sample , namely in NGC 2121 , NGC 2155 and Lindsay 113 .
By combining data from our survey and HST photometry for 3 additional clusters in the Milky Way ( namely 47 Tuc , M15 and NGC 2419 ) , we show that the extent of the MPs in the form of N spread is a strong function of age , with older clusters having larger N spreads with respect to the younger ones .
Hence , we confirm that cluster age plays a significant role in the onset of MPs .