How to marketing website to singles people over 40

I don't get what you really mean but it seems you are looking for people who are at the age of 40 above. I have another question, are you looking internationally or just local? As of now, Social Media network is the better way to find people who has age over 40 both local and international. Looking for them requires time because you need to do it manually unless of you have access to their server where you can easily retrieve all the users who has age over 40.