I've heard this a lot, about adult circumcision.
I was circumcised when I was a baby so I wouldn't know the difference.
Regarding penis length extension by cutting the ligament, the age limit is 40.
After that, no big gains, and risk of the ligament to reattach and go back to 4" again, or nerve damage (erectile dysfunction).
I've heard of great outcomes for procedures to increase volume and girth, by grafting and injecting your own fat, or hyaluronic acid.
There are well-reputed clinics in the US and other parts of the world that are exclusively specialized in how to make your junk look better.