Are there any suggested username conventions?

I am currently designing a form for a registration to a portal which contains very personal information. I am exploring the idea of having a suggested username(s) to be presented to the user to choose if they struggle to create their own one.

There are two reasons for this: 1. The people using it are older, 50-60 years old and are not so tech savvy. 2. Due to the average age of the people using it, I want to to make the Registration as seamless as possible and reduce errors while choosing a username.

My question is: Are there any good conventions for displaying this in forms?