Chances are, your first hike won't be under circumstances where it's dangerous to wear jeans or have the wrong gear. Also, the drawbacks of jeans can be experienced just going for a walk or being outdoors year-round.

I hiked in jeans or shorts until I was about 50. Today, I wear hiking pants instead of jeans for everyday life. The benefits are noticeable. They last a lot longer, don't take stains as easily (bike chain gunk), and being quick drying means I don't have to worry as much about getting wet when I'm out.

Don't go on a long dangerous hike as the first thing you ever do outdoors.