Estimated at around 30 years, it's accepted as the average period between birth of parents & their offspring
[DOC] [TLE] Multi-year lactation and its consequences in Bornean orangutans ... [PAR] Multi-year lactation and its consequences in Bornean orangutans (Pongo 
pygmaeus wurmbii) ... (Pongo pygmaeus wurmbii) over their average 6.5-year 
lactation period.