Whether they will be more mature or not will all depend on the growing conditions you provide. The 50 mm pellets are intended for use with large plants - tomatoes, peppers, big perennials, etc. All the other problems with the peat pellets aside, small plants don't usually do real well in the 50mm because they are planted so shallow and never root that deeply.

You can cut the 50mm in half if you want and then use them for more shallow rooted plants.

Dave