Introducing allergens

I just let my daughters 4 month appointment and the doctor mentioned introducing allergens. with my precious baby I did BLW starting at 6 months and introduced allergens then. my pediatrician said that the newest research is saying introduce by 7 months. i guess Im wondering if anyone else has heard this or did this? do I need to introduce all allergens by 7 months? that just seem impossible if I wait to introduce solids until 6 months