Act as a certified nutritionist with 10 years of experience in mineral metabolism. Explain the critical role of manganese in human metabolism, focusing on its involvement in [enzyme activation], [bone development], and [antioxidant defense]. Provide a detailed breakdown of how manganese deficiency or excess can impact [specific metabolic pathways], such as carbohydrate metabolism or lipid synthesis. Include [dietary sources] rich in manganese and recommend [daily intake levels] for different age groups. Use scientific references to support your claims and offer practical advice for maintaining optimal manganese levels through [balanced nutrition].