Why do Indians touch old people's feet (4 photos)
There's an ancient tradition in India of touching the feet of elders, usually very old, that old. This is done in almost every Hindu family, even the most modern ones, and even those living far abroad. That's how deeply this tradition has permeated everyday life. 
How beautifully the foot is painted, I WAS PREPARED
Indians believe that when a person bows and touches the feet of an elder, their ego is suppressed. After all, this gesture expresses respect for the age, experience, achievements, and wisdom of the person whose feet are being touched. There's even a word for this—Charan Sparsh. It's believed that when your fingertips touch another person's feet, a closed circuit is established that connects your energies (very Hindu). The elder gives, and the younger receives more. 
You can do it standing, but not everyone has the flexibility to bend to the floor without bending their knees.
Those older than you have walked this earth longer than you, lived longer than you, and thus accumulated much wisdom and experience. Therefore, if you touch all the dust on their feet, you will touch their accumulated wisdom. It's a special sign of kindness if an older person places their hand on your head when you bend down to their feet. It's a blessing, and it also closes the circuit! 
A drawing from a chronicle, such an old tradition. And LOOK AT THEIR EYES!
Not everyone can be touched.
Touching the feet of parents and grandparents is obvious. It's socially acceptable to touch the feet of a respected teacher or an older brother who has become a role model for you. Well, everyone has seen at least once how all the Hindus line up to touch the feet of the next spiritual guru. Most often, they touch feet when asking for a wedding favor or thanking their parents at a wedding. Or when asking for a blessing for a long family trip, when they're a little afraid to leave and want to take home at least a little bit of someone else's wisdom. 
Many Indians have a wedding photo like THIS; everyone's happy.
By the way, touching the feet of relatives on your mother's side of the family is forbidden. This is due not only to patriarchal norms, but also to the fact that women's feet are considered very erotic. And that means those relatives have slightly provocative associations. But if it's your grandmother, then it's okay. You have good intentions!
