들다 does several jobs and three appear here. A thought or a question comes to you: 보면 드는 생각 (the thought that comes when you watch), 외국인들 보면 드는 궁금증. 나이가 들다 is growing older, and the ladder phrase 나이가 들면 들수록 ('the older you get, the more...') turns up four times. And 들다 is lifting — 너무 무거우니까 들 사람이 없잖아요, nobody can lift it.