What is the reason to touch the elder person's feet for blessing?

Question

In India, it is tradition of touching feet of a relative who is elder in age (like grandfather/mother, uncle/aunt, in-laws) for blessing.

What is the reason/story behind this ?

Answer 1

Taking darshan by touching the feet is an old vedic tradition. The Laws of Manu say:

II. 71. At the beginning and at the end of (a lesson in the) Veda he must always clasp both the feet of his teacher, (and)...

II. 72. With crossed hands he must clasp (the feet) of the teacher, and touch the left (foot) with his left (hand), the right (foot) with his right (hand).

It was over time extended to others one should consider as superiors as well.

Answer 2

Well the reason for touching the feet of elders is simply because that’s what is the prescribed Sanatana Dharma in various Dharmashastras. However, the significance (most likely Yogic) of the same has been mentioned in the Manusmriti:

On an elder approaching, the vital breaths (Prana) of the younger rush outward; and he recovers them by the acts of rising to meet and salute him.
—Manusmriti 2.120

On the elder’—the person of higher age—‘approaching’—coming up,—‘the vital breaths’—the sources of life, the inner airs—‘of the younger’—‘rush outward’—move out; i.e., giving up their functions, they intend to cut off his life. When however he rises to meek him and salutes him, the breaths proceed, as before, to sustain his life. - Medhatithi’s Commentary

The fruit (maybe another significance) of saluting the elders feet is mentioned in the very next verse:

For one who is in the habit of saluting and constantly revering elders,— four things prosper: viz., longevity (Ayu), merit (Dharma), fame (Yasha) and strength (Bala).
—Manusmriti 2.121

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Besides the obvious ones i.e. Guru, immediate ascendants, and siblings, the text also provides a whole list (not exhaustive) of elders to propitiate:

1. Maternal uncles, paternal uncles, fathers-in-law. - (Manu 2.130)
2. Mother’s sister, father’s sister, maternal uncle’s wife, Mother-in-law (Manu 2.131)
3. The brother’s wife (Manu 2.132)

Answer 3

This is because the same has been prescribed in our scriptures. Gautama Dharmasutra verses 6.1-6.3

1. (To salute) every day on meeting (by) an embrace of the feet,

2. And (particularly) on return from a journey,

3. (Is prescribed in the case) of parents, of their blood relations, of elder (brothers), of persons venerable on account, of their learning, and of the Gurus of the latter.

Please note that one of the existing answer cited Manusmriti for the reason behind touching feet of Gurus. But it didn't delve into touching feet of elders, parents etc.