In reality, cats live around 16 years (if not killed in accidents or by diseases); but in the Warriors series, they seem to live half of that. For example, Mousefur was a 'young warrior' in Into the Wild (let's say 2 years old); but retires in Starlight (6 years old - see here for timespan), and close to death in OTS (8 years) - and I can bring many other examples. Also, many people expect Brackenfur, Thornclaw, Cloudtail... to retire in OTS; but they are only 6 years old at that time (about 40 years in 'human age').
Was this not thought over by the authors (as many other things)? Or they postulate that Warriors live only a few years, so they can get rid of many characters in a short timespan, to introduce others?