I suspected that was what the point of the OP's post was, so I didn't respond initially. There are a few dads on the board, but I'm pretty sure all are married.
I'm also not sure about dating sites as I chose not to become involved in another relationship after husband died.
I know a LOT of them advertise if my email and Facebook feed are any indication and I'm sure there are service that rate them and review sites.
I also know that there are sites that cater to single parents with younger children, and I wouldn't be surprised if there aren't those that cater to older divorced or widowed folks with adult children. Google around enough and you should be able to find some decent sites amongst the inevitable weirdos.