Protein, calcium, iron, vitamin B12 and zinc can be low, especially if all animal foods are excluded. Plenty of carbohydrate-containing foods are needed, eaten at each meal and snacktime, as part of a varied diet. For individual advice, consult an Accredited Practising Dietitian. One egg a day, if desired, would be reasonable for both adults and children. Your requirement for calcium is 1000mg per day, until you are 19 years old when it decreases to 800mg per day.
Calcium is important for healthy bones and has other functions.
Metabolism I've heard that if the more frequently you eat, the faster your metabolism. Dietary guidelines for children and adolescents. Australian Government Publishing Service, 1995. Gibbons, K., Chief Dietitian, Royal Children's Hospital, Melbourne. Here is a sample of the latest studies in nutrition and the elderly.