Genesis 17:24

And Abraham was the son of ninety and nine years when he circumcised the flesh of his foreskin.

ואברהם בן תשעים ותשע שנה, when he received the most recent prophetic vision he was 99 years old as already mentioned in verse 1. This had been at the end of 99 years after his birth, so that when he was circumcised he was still 99 years of age, and had not entered the 100th years. The Torah writes this in order to reinforce the report that he carried out the circumcision with dispatch, and did not wait until he had turned 100 years old.

בהמלו בשר ערלתו, if we were to say that the word בהמלו is in a passive mode. We would have to ask how it could conclude with the pronoun ו which introduces an action by him on the flesh of his foreskin. We never find that a passive mode is followed immediately by an active mode. If, on the other hand, we are to understand the word בהמלו as standing on its own, without direct relationship to the words בשר ערלתו, or if the Torah had written בהמול בשר ערלתו without the pronoun ו, we would not have a problem with the text as it is before us. One could perhaps resolve the problem of the text that we have by saying that the expression בהמלו describes a condition Avraham experienced as a result of his foreskin having been circumcised. We encounter a similar construction in Isaiah 1,30 where the word נובלת describes the condition of leaves of the tree described, i.e. they are shriveled or have wilted. The word is an intransitive verb, and the terebinth referred to as the trunk to which these leaves belonged is certainly not subject to wilting or shriveling. One could argue similarly, that Avraham was now considered נמול, (verse 26) circumcised, seeing that the flesh of his foreskin had been removed. In a similar manner we can also understand the words קרועי בגדים in Samuel II 13,31. The clothes of the men (David's servants) were torn, not the men themselves. The same is true of Samuel II 15,32 where the word קרוע does not refer to Chushai but to his tunic which was torn. Jeremiah 41,5 has a similar construction, מגולחי describes the condition of these men after their beards had been shaved off.