According to This, and if it's average height (5'9"), it has a sedentary daily calorie expenditure of 2,737 calories. I'll start at 10 years old and average height/weight and assume it's male, and assuming linear weight gain.    Age Height Weight (lbs) Calories/Day Calories/Year Calories Above to raise weight Total Calories Total Accumulated     10 4'7" 70 1375 502,219 87,500 589,719 589,719   11 4'10" 95 1543 563,581 87,500 651,081 1,240,800   12 5'1" 120 1749 638,822 87,500 726,322 1,967,122   13 5'3" 145 1917 700,184 87,500 787,684 2,754,806   14 5'5" 170 2086 761,912 87,500 849,412 3,604,218   15 5'7" 195 2254 823,274 87,500 910,774 4,514,991   16 5'9" 220 2422 884,636 87,500 972,136 5,487,127   17 5'9" 245 2552 932,118 87,500 1,019,618 6,506,745   18 5'9" 270 2682 979,601 87,500 1,067,101 7,573,845   19* 5'9" 295 2812 1,027,083 87,500 1,114,583 8,688,428    *Esitmated