Friend looking to immigrate to Belgium (Brussels)

Hi all, I have a friend who is looking to immigrate to Belgium. He is an American citizen. However, he is not looking to work for an employer in Belgium. He has significant savings, and has his own source of income from remote things he does in the United States. He basically want to move to Belgium for the lifestyle. Would he be eligible for a long stay visa?

Thanks in advance,
-David B.