People are sexually active much earlier now and are much more comfortable with their sexuality. No, you can't really crush walnuts. In fact, there is an old urban myth in which a couple was having sex and the girl got scared and her vagina clamped down and trapped the guy's penis. They had to go to the emergency room to get disconnected. This never happened.
Sex is a serious matter.
I always recommend that you postpone it for awhile to give you and him a chance to get to know each other better. When sex enters a relationship, the relationship usually revolves around sex. Take it easy and go slow. You can tell him that you want to head in that direction but that you are not there yet. The first step is to make sure that your partner agrees you need to spend more time together.