As per Sargas 15-17 of Srimad Ramayana, after Lord Vishnu agreed to take birth as a son of King Dasaratha, Lord Brahma ordered as follows:
सत्य संधस्य वीरस्य सर्वेषाम् नो हितैषिणः |
विष्णोः सहायान् बलिनः सृजध्वम् काम रूपिणः || (Bala Kanda, Sarga 17, Shloka 2)
Let mighty and guise changing helpmates be procreated to that truth abiding and valorous Vishnu who is the well-wisher of all of us.
वानरेन्द्रम् महेन्द्र आभम् इन्द्रः वालिनम् आत्मजम् |
सुग्रीवम् जनयामास तपनः तपताम् वरः || (Bala Kanda, Sarga 17, Shloka 10)
Indra procreated the lord of vanaras, namely Vali, who by his physique is like Mt. Mahendra, and the highest humidifier among all the humidifiers, namely the Sun, procreated Sugreeva.
Within 1 (one) year Sri Rama was born. So, Vali, Sugreeva, Sri Hanuma and Sri Rama should be more or less of the same age.
However, other descriptions in Srimad Ramayana do not corroborate the above narration.
Nowhere in Ramayana, the ages of Vali and Sugreeva are mentioned.
Vali never assisted Sri Rama in the annihilation of Ravana, as per Srimad Ramayana.
Vali had a severe fight with a demon named Dhundhubi. When Vali killed that demon and hurled the dead body of Dhundhubi, it fell in Sage Matanga's hermitage. Sage Matanga cursed him to the effect that if he or his friends enter the surroundings of his ashram they will fall dead. This incident indicates that Vali was a grown up person at that time, i.e., around 20 years at the minimum and Sage Matanga was alive.
After the demise of Sage Matanga at an old age, the disciples of Sage Matanga lived in that Ashram. Sabari, a female attendant to those disciples, used to serve them with devotion.
By the time Sri Rama reached Chitrakoota, his age was only around 25 years. And at the same time, the disciples of Sage Matanga, who are very old, attained heaven.
चित्रकूटम् त्वयि प्राप्ते विमानैः अतुल प्रभैः |
इतः ते दिवम् आरूढा यान् अहम् पर्यचारिषम् || (Aranya Kanda, Sarga 74, Shloka 14)
Divine aircrafts of unequalled refulgence have lifted those disciples of Sage Matanga in whose tendance I was, to welkin on your arriving at Chitrakuta
That means a considerable period of time, between the Dhundhubi incident and the time when the disciples of Sage Matanga attained heaven, i.e, a minimum period of 40 to 50 years must have elapsed and Vali might be 60-70 years old when Sri Rama reached Chitrakoota. By the time he reached Kishkinda he was 38 years old and Vali might be 80-85 years old.
By the time Sri Rama reached Kishkinda, Vali had a son by name Angadha, who was a grown up person.
Hence, in my view, Lord Brahma ordering the Devatas to procreate vanaras, was a prakshipta, an insertion made at a later date.
Am I right?