Is there any biological constraint to attain Nibbana? This question may look like a copy of this question, but I am asking in a broader sense including age limit. 

The historical reference of a person attaining Nibbana in oldest age is Joshu, apparently, he became enlightened at the age of 80 and then settled down to become a master. But he looks like some kind of exception. 

Gotama Buddha attained Nibbana in His 30's, from scriptures all the others seem to be between 30's to 40's nobody is told to be very old. Neither was Bodhidharma, Zen patriarchs, Tibetan masters like Milarepa, Marpa all seem to be somewhere in 30's or 40's during their Nibbana, based on what all things they did after that. 

So, I am asking is there any biological limitation, age limitation, for Nibbana?
As far as I know the youngest arahant in the sutta's was 7 years old. Unfortunately I don't remember which sutta this is.

So, I would say: no, there is no limitation to reaching arahanthood or nibbana.