Dwarves and ageing
Dwarves remain too young, regarded as too tender for really hard work, or fighting, until 30. At the Sack of Erebor, Thorin Oakenshield at 24 was considered "not yet war-worthy". Dain Ironfoot was very young at 32 to fight at Azanulbizar, a "stripling", and even Thorin Oakenshield at 53 was young, although war-ready. Dain is of course an exception, being the epitome of the Dwarven Hero. After 30 dwarves harden and take on the appearance (by human standards) of mature age quickly. By 40 all dwarves look alike in age and retain such, barring scarring and maiming, until the beginning of old age around 240.
Appearances and genetics aside, socially dwarves are not considered fully mature until around 100. Before this they usually live with or near their parents, and accompany their elders on journeys and such. Thorin Oakenshield was considered "a great dwarf of a great house" at 95 when he assumed the rule of the Ered Luin halls. Gimli was in "full manhood" when he joined the Ring Quest, although at 62 Thorin Oakenshield considered him too young to join his father on the Erebor Quest - although *he* thought he was ready. Fili and Kili, both thought young by the Questers, were 82 and 77 in 2941. Most dwarves marry quite late in life, and very rarely before 90 or more. Having up to four children is rare; more, never heard of. Families never force or arrange marriages.
A dwarf lives, on average, about 250 years. 240 is considered the beginning of venerability - between 40 and 240 the capacity for toil for most dwarves is equally great. On average, around 240 a dwarf will begin to exhibit signs of age, wrinkles and whitening hair, etc; they never lose their hair naturally, however - baldness being unknown among dwarves. Almost the only physical disorder, being immune to disease, known among dwarves is corpulence, and then only when living prosperously, in such cases prone to go to fat at 200 or before.
"Old age" usually lasts no more than 10 years (when a dwarfs hair goes white, they're "on the clock"!). Dwarves seldom live short of 250, and occasionally live longer. Those of Durin's line can reach up to 300 years; a 300 year-old dwarf is about as rare as a 100 year-old human (note: NOT a modern human with the benefit of medical science).
In the Erebor culture, new players are required to choose an age between 90 and 180. Experienced Dwarven players may apply for a character between 40 and 240. All other ages are restricted to honour and feature characters.