Whoever accepts this statement of Bhagavat Purana will have to also accept that Krishna was ~27 years old** at the time of killing Kamsa.
So, those who take each word of Bhagavat Purana literally, think again!
The reference from Bhagavat Purana is as follows:
Srimad Bhagavat Purana 11.6.25
Word for word:
yadu-vaṁśe — in the family of the Yadus; avatīrṇasya — who has descended; bhavataḥ — of Yourself; puruṣa-uttama — O Supreme Person; śarat-śatam — one hundred autumns; vyatīyāya — having passed; pañca-viṁśa — by twenty-five; adhikam — more; prabho — O Lord.
O Krishna, You have descended into the Yadu dynasty, and thus You have spent one hundred twenty-five autumns.
** ‘The Year of Mahabharata War: Additional evidence from Astronomy, Geology & Anthropology’ (book in works)