If I was going to incorporate age into Dragon Warrior, I'd do it by:
Starting character at age 12, or so.... You're a young peon killing slimes with a bamboo stick for goodness sake. STR -4, DEX -4, CON -4, INT -4 for reduced stats.
Each hour of game play, the character ages a year. (5 minutes game play represents a month.) Physical stats go up 1 per year for the next 4 years. Mental stats go up by 1 per every two years for the next 8 years. Give a nice in-game notification/pop-up to make the player aware of this event.)
At this point, your character is basically an adult and won't automatically "grow/wither" for the next twenty years or so. Around the age of 40, physical stats slowly decrease but mental stats increase. (Age makes us slower/older, but smarter/wiser, they claim.)
After another 20 years or so, the mental growth stops...
Another 20 years and even the mental stats start to drop...
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I don't think most people play Dragon Quest for countless hours, but it adds an element of character growth that stands out as slightly different from the original, without being something which would make game play frustrating to the point of unplayability.