Simple designs are used by kids while intricate and complicated designs are used by brides and young girls. May be your are thinking that it is really difficult work to use or make a design of mehndi on your hands and feet,but it is so easy and you just need some practice to make mehndi designs.
I am sure you heard that sentence “Practice makes a man perfect” and thing is applicable here. If you take some interest on making designs of mehndi then it will be very interesting and easy for you.