Antonyms for the phrase "growing feeble" would include "strong," "vibrant," "energetic," "robust," "resilient," and "sturdy." These words paint a picture of health, stamina, and vitality. Rather than fading in strength, someone who is strong is powerful, resilient, and full of life. Vibrancy suggests a colorful, lively energy that translates into brightness and positive forward motion. Robustness implies unwavering mental and physical toughness. Sturdiness suggests a firm foundation of strength and stability. By using these antonyms, one can shift the focus away from feebleness and towards the opposite end of the spectrum, highlighting the importance of staying healthy and strong at any age.