I Agree physical fitness is a must. I recommend the more functional type exercises (Cross fit, SEAL Fit, etc) over traditional free weight work outs. I am no expert by any sense of the term. In my own experience the traditional gym / free weight work out may build strength, but dose not necessarily translate to what you may need during self defense. I have had the experience where I felt fit but after engaging in an altercation I experienced the old cliche "I was sore in places I didn't even know I had". Cross fit and other functional routines, work out those places you don't know you have. Most of these work outs are scalable so that yo don't have to be SEAL Fit to do a beneficial and functional SEAL FIT work out. I am 51 years old, believe me I scale back on the intensity but still get a good work out.
attached is a link to one of my favorite exercises. WTSHTF, being able to pick yourself up off the ground may be alot more helpful than being able to curl big weights.