Can some palpitations be normal and not dangerous at all, or do all of them carry some sort of risk?

Palpitations: Yes, not all palpitatios are dangerous. There are arrhytmias which are benign and are responsible for palpitations

Palpitation Sx: Palpitations are an awareness of extra heartbeats which most of us have. The sensation can be single or multiple and can sometimes last minutes. Different people may feel other symptoms along with them such as dizzy, lightheaded or short of breath. The palpitations are almost always atrial or ventricular premature beats. Usually benign but they are also found with abnormal hearts.

Most: At your age most are normal. If the frequency and the rate...crosses certain parameters, they are abnormal. If the heart is structurally abnormal.....any palpitation is abnormal.