I have a friend who's applying for a F1 visa. His parents brought him to the US when he was little (8.5 years old), but he left once he turned 18 with his parents and hasn't attempted to re-enter the US since. (Actual age at departure 18 years and 20 days). He's now 26 and he wants to attend a graduate program in the US.
Your friend started accruing "unlawful presence" on his 18th birthday. As he left within 180 days, he didn't acquire a ban. If he had left after 180 days, but left before a year, he would have acquired a three year ban which would now lapsed. If he had left on or after his 19th birthday, he would have acquired a ten year ban which would still be in force.
The real problem is:
What’s more, an overstay on one’s record can make it difficult to obtain many other nonimmigrant visas or immigration benefits, since the immigration authorities will have to first be convinced that you will abide by the terms of your next visa.
The quotation is from: https://www.alllaw.com/articles/nolo/us-immigration/visa-overstay-minor.html
It is vitally important that your friend is very careful to be completely truthful when he fills in the application form. If he is found to have not told the truth (even if it was, in fact, by accident), he is unlikely to ever be able to get a US visa.