I think my dad was a little aprehensive of flying with me...he even said i couldn't take my mum...so, I took my mum and then he was desperate to go!
I think it was nerves/not knowing what to expect or just a 'flying with family' thing as he had already been up with a friend of mine and had loved it.
revilo_rehsif, why not teach you dad how to basically fly the aircraft? I got my 70 y.o Gran doing a few turns and straight and level and she can barely see out. My Mum and Dad are pretty good, my brother, a natural!