Meaning:
“光” means “only,” “想” means “to think,” and “青年” means “young people.” This term is quite literal, and refers to young people who have many ideas but never put any of them into action. Either because they are lazy or afraid of taking any risk, their ideal life is thousands of miles away from reality.
Example:
A: 今天中午的自助餐小马吃得可真不少。
Jīntiān zhōngwǔ de zìzhùcān xiǎomǎ chī de kě zhēn bù shǎo。
Xiao Ma ate quite a lot at the buffet lunch today.
B: 他不是天天说要减肥吗？原来是个光想青年。
Tā búshì tiāntiān shuō yào jiǎnféi ma？Yuánlái shì ge guāngxiǎng qīngnián。
Isn’t he always proclaiming that he wants to lose weight? It turns out he only thinks, but never acts.