Is it possible that Allah will shade on the Day of Judgment a young man who did not grow up worshipping Him from childhood, but who became committed at the age of twenty and kept supplicating to Allah to count him among those young men who grew up in obedience to Allah?

The meaning of "a youth who grew up in the worship of Allah" is that he grew and was raised in it, not in disobedience, and he will be rewarded with the shade of the Throne for preserving himself. This honor is specific to those who grew up in the worship of Allah, but immense good and great reward are hoped for those who repent and become upright after deviation, for they may be among those whom Allah shades in His shade, because "the one who repents from a sin is like one who has no sin." The seven mentioned in the hadith (definition) are united by their striving against the self and opposing vain desires. The number mentioned in the hadith does not imply exclusivity; those whom Allah shades in His shade are more than the seven mentioned, such as one who grants respite to a debtor in difficulty or forgives his debt. It is permissible to supplicate that Allah records you as one who grew up in obedience to Allah, and Allah answers supplications, forgives sins, and transforms bad deeds into good ones.