I started working with a mature horse on this issue two weeks ago. He was VERY resistant to having his back feet and tail handled (brushed). The closer you are to his body the less likely you are to be kicked. If you reach toward the legs from arm's length, the horse may consider you a predator, and react accordingly. Just run your hands down the legs, massaging gently. Lift the foot and cradle the hoof in your hand close to the ground. Use a little pressure, but let the horse feel as though he can escape.
If he crowds against the fence, gently put your body between her and the barrier and ask her to move over. It is a question of trust and confidence. Talk to her. Tell her she is a very good girl!! She will respond to the positive tone of your voice.
After two weeks, my mature horse is perfectly comfortable with my handling his tail and holding his legs. Just take it slow, but present yourself with confidence. Don't act like a sneaky predator.