Nowadays many people save money to _ for their old age. The source is from my exercise books. The key here is "provide". But I don't think so. I think here "cater" can also meet the need in the sentence here. In my poor opinion, "cater for" has the meaning of "to provide what is required or desire" and here we can interpret the sentence as the meaning: Many people save money to provide what they need when they are too old to earn money in their old age. It seems that it can make sense, isn't it?