Please explain if it is really bad to swallow tooth paste?

Toothpaste. Swallowing a little toothpaste while you are brushing your teeth is normal and nothing to, worry about. Eating toothpaste on the other hand is not a good thing as the Fluoride in it can cause an upset stomach. This is much more of an issue if you are talking about a small child eating a lot of toothpaste.
Not food. Won't hurt you, it's not toxic, but it isn't too smart. Toothpaste isn't food. Use exactly as directed on the label.
It's not a good . Habit to routinely swallow it, but if it's an isolated occurance there should be no problem. Hope this helps.
Not a problem. Potentially toxic dose = 6 mg of Fluoride per kg of body weight. For a 70 kg adult, the lethal dose of 4.2 grams of Fluoride would require swallowing at least 4 liters of toothpaste, or 20 whole 200 ml tubes of toothpaste, which is impossible. You are safe.
Not bad but . Not encouraged as excess flourid in paste can have potential harms.
No. At your age, not really. Young children should not because we don't want them to get too much fluoride.