Many of a true dragon’s abilities, attacks, and other statistics improve as a dragon grows older. These increases are divided into 12 age categories—as a dragon ages, its base statistics change as noted on Table: Dragon Age Categories.
Size: This shows how many size categories by which to increase the dragon’s base size, depending on its age (from Tiny to Small, Small to Medium, and so on). A true dragon does not gain the standard increases to ability scores when it achieves a larger size—instead, true dragons gain ability score increases according to their age category, as indicated on the Dragon Ability Scores table.
Hit Dice: This shows how many additional Hit Dice a dragon gains over its base Hit Dice as it grows. Increases to Hit Dice grant extra hit points, feats, and skill ranks as well as increase the dragon’s base attack bonus and base save bonuses. Dragons have skill ranks equal to 6 + their Intelligence modifier per Hit Die. A dragon’s increases to ability scores for gaining Hit Dice are included in the total ability score increases (see the Dragon Ability Scores table).
Natural Armor: This shows by what amount the dragon’s base natural armor bonus increases with each age category.
Breath Weapon: Each dragon has a breath weapon (see Combat) that deals a base amount of damage. This multiplier increases the number of dice of damage dealt by the dragon’s breath weapon. For example, a mature adult dragon with a base breath weapon that deals 2d6 acid damage would deal 14d6 acid damage (due to the ×7 multiplier).
Emphases are mine. Size, HD (and therefore breath), and even natural armor are all determined by their age category. And since the abilities you mentioned are requisite on size and size is dictated by age category the previously mentioned abilities are dependent on the age of the dragon. Cause: Age category, Effect: everything else
Furthermore, nowhere in pathfinder does increasing or decreasing in size has bestowed additional abilities that you did not already have. Spells like beast form, FotD, Monstrous Physique, etc explicitly say when additional abilities are gained. Enlarge/Reduce Person has no such mentions. Unless the actual or "effective" size change also bestows additional abilities, the dragon gains nothing by changing size via magic.