between age and $U-B$ colour index of a stellar system is possible only in terms of continuously populated IMF. Stochastic effects in the discrete randomly populated IMF begin to play a key role for SSP stellar systems (star clusters) with masses less than $5\cdot10^3-10^4 M_\odot$ [@whitmore2010; @piskunov2011]. This effect is clearly illustrated in Fig. 19 in @gusev2016. Due to the impossibility of finding an age by $U-B$ colour for low-massive clusters, we excluded star clusters with masses $<5\cdot 10^3 M_\odot$ from further consideration (green dots in Fig. \[figure:ub\_logs2\]).

The final sample includes 503 SC-H[ii]{}R pairs in NGC 628, 70 pairs in NGC 3184, 254 pairs in NGC 3726, 40 pairs in NGC 5585, and 577 pairs in NGC 6946. To illustrate the selected objects, we present a couple of postage stamp images of H[ii]{} regions and star clusters in the closest (NGC 5585) and the most distant (NGC 3726) galaxies in Fig. \[figure:map1\]. Our full sample of identified and finally selected star clusters and H[ii]{} regions is shown in Fig. \[figure:map2\] for the NGC 628 galaxy.

Results
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Cluster age versus separation relation {#sect:age_sep}
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Fig. \[figure:col\_dist\] shows a clear linear dependence between the colour index $U-B$ and the separation 