Born August 10, 2001.
14 (was originally planned to have been 15 but fortunately not said on-screen, turns out he was 14) in Civil War in June 2016.
15 (stated explicitly) in Homecoming in September 2016.
16 in Infinity War in May 2018.
Snapped before his 17th birthday (which would've been August 2018) in May 2018.
Returned aged 16 in October 2023 after 1965 days. This makes his biological age now as if he were born December 27, 2006, However, in terms of birthdays, his next birthday would now be August 10, 2024, and if he considers this his 17th birthday (which he does), then by birthdays, it's now as if he were born August 10, 2007.
16 (both biologically and by number of birthdays) in Endgame in October 2023.
Biologically 17/still only had 16 birthdays, and considers himself "16" (explicitly stated) in Far from Home in June-July 2024.
17 (both biologically and by number of birthdays) in most of No Way Home in late 2024.
Tom Holland also described Peter as a 17 years old kid in this movie.
10th August 2001-Peter Benjamin Parker is born
June 2010-Peter is 9 years old and meets Tony Stark/Iron Man
December 2015-Peter becomes Spider Man and is 15 years old
May 2016-Peter is recruited by Tony to join his team against Steven Rogers/the first Captain America
October 2016-Peter Parker is 16 years old and defeats Adrian Toomes/Vulture with help from Tony becomes a unofficial Avenger
May 2018-Peter is 17 years old and becomes a official Avenger and battles Thanos with Tony,Drax,Quill,Mantis and Strange and gets snapped or blipped by Thanos
October 2023-Peter is still 17 got unsnapped by Hulk from Titan and fights in the battle of Earth against Thanos
July 2024-Peter is 17 battles Mysterio and gets unmasked as Spidey
PETER PARKER IS 17/18 IN NO WAY HOME
If we are to count the time he was gone, he'd be 22.
Actually he would be 23.
2024-2001 = 23
What do you think?