Gito is doing much better than when he was found suffering from dehydration, malnutrition and a skin infection, but his caregivers warn there is a long road ahead.
IAR programme director for Indonesia, Karmele Llano Sanchez, said Gito would still need to take part in "jungle school" - a scheme designed to prepare orangutans for life in the wild - before he could be released.
"It's going to take five to seven years before he is ready to be released into the wild," she told AFP.
Bornean orangutans are classified as endangered species by the International Union for Conservation of Nature and are protected under Indonesian law.
But their jungle habitats are being destroyed by the rapid expansion of palm oil and pulp and paper plantations, while locals view the apes as pests and sometimes target them.
Hundreds of Bornean primates were also rescued last year as massive, smog-belching forest fires ravaged the island. The fires, started to clear land for plantations, are an annual occurrence, but in 2015 were the worst for some years.