וְאַבְרָ֕ם בֶּן־שְׁמֹנִ֥ים שָׁנָ֖ה וְשֵׁ֣שׁ שָׁנִ֑ים בְּלֶֽדֶת־הָגָ֥ר אֶת־יִשְׁמָעֵ֖אל לְאַבְרָֽם׃
Avram was eighty-six years old when Hagar bore Yishma'el to Avram.
לְשִׁבְחוֹ שֶׁל יִשְׁמָעֵאל נִכְתַּב, לְהוֹדִיעַ שֶׁהָיָה בֶּן י"ג שָׁנָה כְּשֶׁנִּמּוֹל וְלֹא עִכֵּב:
This is written to Yishma'el’s credit, pointing out that he was thirteen years old when he was circumcised and yet he raised no objection.
I don't understand what Rashi is saying here. We have an explicit verse (Bereishit 17:25) that tells us that Yishma'el was thirteen years old when he was circumcised.
What is Rashi inferring from Bereishit 16:16 which we would not know from Bereishit 17:25?