10 years ago, colonoscopies were every five years.
According to my doctor, only those with Breast cancer in their families can get a baseline earlier than 50. And IIRC, about 8% of new breast cancers have a familial connection.
It may well depend on a doctor but all anyone can really go by is personal experience...This from 2014:
“”The American Cancer Society recommends that a woman obtain her first baseline mammogram at the age of 40. After that, she should receive a yearly mammogram.””
http://www.medicinenet.com/mammogram/article.htm
As for colonoscopies - I had one in 2003 with the written results to have another one in 10 years which I didn’t do until a doctor asked me in 2014 why I hadn’t done it....