"私は決して大人になりたくない。"

Simplified Meaning:

The speaker is expressing a desire to keep the freedom, joy, and imagination that are usually more common in children. They're not interested in taking on the responsibilities and worries that often come with becoming an adult. Think about how kids are excited to play, imagine new worlds, and feel happy with simple things. Adults often have to focus on work, bills, and serious matters, leaving less time for fun and creativity. By wanting to stay young at heart, the person wishes to hold on to that sense of wonder and avoid the stress and complexity of adult life. If you apply this to your life, you can try to keep a playful attitude, make time for fun activities, and not let the pressures of being an adult take away your happiness. For example, even if you have a busy job, you can still find moments to enjoy hobbies, laugh with friends, or simply daydream.