她是我年少时最冒险的梦
[tā shì wŏ nián shăo shí zuì mào xiăn de mèng]
'She was my most adventurous dream when I was young.' Here it expresses how someone has deeply influenced or left unforgettable memory during a youthful period. With 'her', it could mean a girl who represents the speaker's longing and pursuit in those days.