Online dating not interested

Of course, it’s normal. You can reject others on a dating site. It’s just a part of the game.
It’s not rude to tell a man that you are not interested in him. He should appreciate your honesty if he is a mature man. If he goes furious, that means he is very childish and mean. You don’t want to be with someone like that.
You can ignore his message if you don’t like him and he will get the message – silence means rejection. Normally, he wouldn’t keep sending messages to you anymore because most dating sites are not free (he wouldn’t want to waste his money on radio silence).
But if he does keep sending you messages, you have to block him. If he keeps harassing you, you must report him to the customer service team of the dating site. The customer support team should work 24/7 online or via phone.
My suggestion is joining more than one dating site because you’d better maximize your chance of finding someone suitable fast. Your time is your most valuable asset. If you think you are young, soon you will be old; if you think you are old, soon you will be older.