tā / bǐ / nán yǒu / dà / wǔ suì / suǒ yǐ / zhè / shì / yí duàn / jiě dì liàn

她比男友大五岁，所以这是一段姐弟恋。

She is five years older than her boyfriend, so this is an older-woman-younger-man relationship.