pming
Legend
Hiya!
"Depends on the edition".
BX/BECMI: No real 'age' categories...just sizes; Small, Large and Huge, but has an additional modifier of being "...found with up to 3 Hit Dice smaller or larger than the average given" (e.g., a Large Black dragon can have between 7+3 HD, to 13+3 HD, with their base 10+3 HD). This is probably the BX/BECMI version of 'age'.
Other "D&D" I like Hackmaster 4th's (the 'first' HM published, not the newer one) age categories. There are 13 of them (0 to 12; Egg, Hatchling, Very Young, Young, Juvenile, Young Adult, Adult, Mature Adult, Old, Very Old, Venerable, Wyrm, Great Wyrm...for age3s -1 up to 1201+). It's worth noting that HM4 does NOT mess around with dragons! O_O You think a "Great Wyrm" from 5e with 500hp is tough?... ...try 2,000 to 3,000hp or more for a HM4 Great Wyrm!
^_^
Paul L. Ming
"Depends on the edition".

BX/BECMI: No real 'age' categories...just sizes; Small, Large and Huge, but has an additional modifier of being "...found with up to 3 Hit Dice smaller or larger than the average given" (e.g., a Large Black dragon can have between 7+3 HD, to 13+3 HD, with their base 10+3 HD). This is probably the BX/BECMI version of 'age'.
Other "D&D" I like Hackmaster 4th's (the 'first' HM published, not the newer one) age categories. There are 13 of them (0 to 12; Egg, Hatchling, Very Young, Young, Juvenile, Young Adult, Adult, Mature Adult, Old, Very Old, Venerable, Wyrm, Great Wyrm...for age3s -1 up to 1201+). It's worth noting that HM4 does NOT mess around with dragons! O_O You think a "Great Wyrm" from 5e with 500hp is tough?... ...try 2,000 to 3,000hp or more for a HM4 Great Wyrm!
^_^
Paul L. Ming