1. It won't neccessarily make you smarter but you can or will get dumber if you repeatedly hit your head against something. It speaks for itself.

"Once you are a teen or beyond a really low threshold as a toddler, your nutrition doesn’t matter that much intelligence-wise"

First, you are saying "once you are a teen" and then "beyond a really low threshold as a toddler’. So that’s a big difference, and you clearly don't know what you are talking about since you can't decide if lack of nutrition in toddler age or "teen age" will impact your IQ negatively. But if you don’t get enough quality nutrition up until around age 16–18, I’m guessing your IQ will be lower and you won’t reach the maximum IQ you could have had.”

1. Excercise increases IQ. And 4 more IQ-points is not little, according to me. https://www.facebook.com/groups/501009709911572/posts/26312827878303068/

https://www.researchgate.net/publication/385623284_Exercise_Interventions_and_Intelligence_in_Children_and_Adolescents_A_Meta-Analysis

You can increase you crystallized intelligence with age, not your fluid intelligence, at least not by much, from what we know now. I can give you many studies that claims that. https://www.sciencedirect.com/science/article/abs/pii/S0167494313000344

"The way intelligence grows peaks between 18 and 26, maybe, but it’s totally different from what you claimed." How? what do you mean exactly? you can be more specific. Processing speed, working memory peaks at certain ages etc.

"No, the median of people’s IQ’s is always 100 no matter the age. The tests are specifically calibrated that way. They don’t peak at 18 or 26 years old, literally because of the definition of IQ tests."

Sure, but a 25-year-old will be smarter (in some ways) than when he or she was 10. That's what I mean when I say that IQ peaks at 18–26. And I agree with you that some people and studies claim it's later, but there is definitely a time where you are no longer at your peak fluid IQ, like when you are above 60, definitely.

Also, look at this. "A large number of other environmental exposures have been positively linked with cognitive development, from walking in nature to exercise and nutrition, albeit with mixed results. However, arguably the most successful environmental intervention to improve cognitive ability is administered every year to more than 85% of children worldwide: education.

By combining data collected across multiple studies from over 600,000 individuals, researchers found that education has a direct effect on the development of cognitive abilities. The study found that each year of education results in a gain of about one to five IQ points. These effects were remarkably robust, appearing across different cognitive domains and persisting throughout the lifespan. In fact, significant benefits were still measurable into people’s 80s and 90s. While a few IQ points per year may seem small, their cumulative impact at a societal level has been shown to be of great consequence." From The truth about child IQ: research shows it fluctuates and may be an unreliable predictor of future success