Just based on what you describe, he sounds both worried about you and completely in the dark concerning where you are headed with your life. In other words, a normal dad.

Don't think of this as explaining yourself. Instead, reveal yourself. Find something to do or someplace to go where he can get a feel for who you are. There was an old Saturday morning cartoon version of Winnie The Pooh where everybody felt bad because Eeyore was sitting on this hill by himself. They try to talk him down, trick him and argue with him, but Eeyore is sitting on the hill. In the end, they all go up to Eeyore on the hill and finally see the amazing sunsets he has been watching while everybody else was being foolish. You need to take your dad up the hill to see whatever it is you see.

I went through the same thing with my dad. He was mad as hell that I was skipping school all day and sneaking out of the house at night to play in bars before I was old enough to drive. He was even less thrilled when he discovered that the band I was playing with was an IRA band from Belfast (it was the '80s and I was a kid, so don't judge). Then one night he followed me and saw me playing on stage - after that he not only supported me, he started going on adventures with me.

My dad is so logical he makes Spock look like Austin Powers. We drive each other crazy, but we have also learned how to learn from our wildly different perspectives. He sees things I usually overlook or ignore and I see problems from multiple perspectives. Individually we are quirky, but together we make a great team. He is my best friend.

It's not easy to explain yourself, even more so when it is your dear old dad doing the questioning, but you have the opportunity - no, the privilege - to both help him understand and to reassure him that you will be okay. Don't let your emotions take over and go on the defensive. Use your insight to help him really see you.