There is no fixed age at which every Maine Coon becomes calm. Young cats usually change as they mature, but playfulness can remain part of an adult's personality. Activity also depends on the environment, daily routine and opportunities to explore, scratch and interact. If you want a quieter companion, choosing an adult whose behaviour is already known can be more informative than hoping a particular kitten will settle by a certain age. At home, provide appropriate outlets instead of expecting a cat to stop playing altogether.
Short, regular interactive sessions can fit around your routine, while comfortable rest areas allow the cat to withdraw afterwards. Sudden lethargy is different from gradual maturity. If an energetic cat abruptly becomes inactive or reluctant to move, ask a vet for advice rather than assuming the lively stage has ended. Track when lively spells happen: a predictable evening burst may be easier to accommodate with planned play than repeated attempts to stop normal activity.
For product comparisons alongside this advice, see Velvet Nest and Sterling Court litter tray. The details below explain their sizes and uses.
Further reading: gccfcats.org; pdsa.org.uk.
Velvet Nest
Sterling Court litter tray
Taj-MeowHall