Do you know, Sant Dnyaneshwar wrote Dnyaneshwari at age of 15, while Adi Shankara wrote Nirvana-Shatkam at age of 8?

Not only they could understand the knowledge, but could easily cut through these various layers Koshas, Mana, Buddhi, and reach to the Aatma, even before becoming adults..

It’s natural to ask, HOW? Why some people are so fast and find it so easy, while we, even with multiple decades old already, still struggle to even understand few shloka of Bhagavad Gita properly, leave aside breaking through the layers of Koshas.

As expected, why this happens is explained in Bhagavad Gita, (6.43-45)
तत्र तं बुद्धिसंयोगं लभते पौर्वदेहिकम् | यतते च ततो भूय: संसिद्धौ कुरुनन्दन ||
पूर्वाभ्यासेन तेनैव ह्रियते ह्यवशोऽपि सः।जिज्ञासुरपि योगस्य शब्दब्रह्मातिवर्तते।।
प्रयत्नाद्यतमानस्तु योगी संशुद्धकिल्बिषः। अनेकजन्मसंसिद्धस्ततो याति परां गतिम्।।

For spiritual progress, one starts from where it left in earlier life, and if one already had achieved elevated levels in earlier life, they strive even harder in next the lives to make even further progress, and find it easier to reach destination.

In case of Dnyaneshwar, Adi Shankara and many others, they were already at highest level of spiritual progress in earlier lives, with few steps to reach destination. So, their layers of kosha, were already extremely thin for them to break through and reach to the Aatma. No wonder we call them avatars.

Lets learn from these examples, not waste the opportunity we have got in this life, and make as much progress as we could, that way we could be inching towards the ultimate goal.

All the Best!