i can explain this answer in hindi well. But, i think you are learning hindi, thus i will try to write in english.
See, this religious act started with teacher-student relation. when a student used to touch his teacher's feet then, he gives all his bad habits to teacher and takes positive energy from teacher. A teacher will never touches his students feet. THus a young person touches his elder's feet. It shows dedication of elder people that they take negative energy from their youngers and still they feel happy. this is our hindu culture, to give happiness to others. we dont want hatred. only love and peace everywhere.