I am not sure. According to the movie, he is 15 months younger than Gwen, so if we can find out her age, we can know his. Personally, I think he is 15, but that is just my opinion.

This is really late, but in Ultimate Spider-Man, Web Warriors, he is 13. I just realized that if he were 15, he would be the same age as MCU Peter, so I don’t think that’s true, but I also think he is in high school........ sooo...... I don’t know.

In the movie he says a bunch of stuff about going through puberty, which happens at about 9-16(more likely 9-13, but we can't rule out 14-16), and he's been in middle school for at least one year, so he's in 7th grade or 8th grade. He's smart, so he probably wasn't held back, and he might've skipped a grade. He could be anywhere between 12-15, since he's in 7th-8th grade. I don't think he looks like he's 12 or 13, so probably 14 or 15. Gwen says she has been Spiderwoman for 2 years, and she's also in middle school, and 15 months older than Miles. She's probably in 8th grade, probably 16. Miles, at 15 months younger than her, is over a year younger, so probably 14 or 15.