I just went and read your other question. This DID happen to my grandmother 5 years ago. It seemed like my grandpa had been dead for 2 seconds and she found this guy. We just KNEW he was going to take her for everything she had. He was 25 years younger and was about to retire from a teaching job. He didn't have a house, lived in a mall apartment, admittedly didn't have much money, and didn't have any family near by.
The advice people gave that you quote here, really is right on! You should by all means express your concern to him and be honest with how you feel about the situation. After that, what he chooses is what he chooses. We all tried to stop the relationship time and time again. She DID stop talking to us. She wouldn't return our calls. She wouldn't answer her door, she changed the locks. (The locks being changed after the guy broke up with her.) She was angry with us, she wouldn't have anything to do with us. Two years ago she started getting dementia. She stated sliding mentally and was still mad at us. Now she has full blown Alzheimer's and lives in a care facility. For the last 5 years our only interaction with her has been her being mad at us for stepping into her personal decision, and now her not remembering us.
While those people weren't in a similar situation, their advice was right. He IS an adult. He DOES get to make this choice. He WILL be angry, and it WILL be very bad for your relationship. What's funny, is in the 2 years the MUCH younger guy didn't take any money from her. He broke up with her, because his mother was ailing and he moved back home. He never took a cent. She was happy. And, we were complete Jerks for trying to treat her like a child. The only way she lost any dignity, is because we didn't give her any credit and treated her like she couldn't make a decision. Yes, this woman might be after money, but she also might not. Yes, he might be acting careless. YES, it is HIS choice to do so. NO you have no right to meddle.
I get that how people answered wasn't exactly what you expected, or what you wanted. (I know, because people gave me the same advice and I hated it.) They were right, though. You shouldn't ignore their advice, because it's not what you wanted to hear. You should take it to heart, and realize that you're wrong and their advise was actually wise.