Aine,

The Oxford English Dictionary describes a Hooray Henry as being: a rich but ineffectual young man

That's a reasonable definition. I'd go further in saying that a Hooray Henry is a rich, upper class man who is somewhat stupid, and has never had to work in his life. Prone to saying (in upper class, southern english accent) 'gosh how super'

Think of a male version of Princess Diana, and you'll get the idea

Clare