Sebastian writes, "I am in 50s and my wife is in her early 20s and I want to start the paperwork for her green card so that she can join me in the US. Do you think this huge age difference will make USCIS suspicious? What can I do to satisfy their requirements?"
In marriage based permanent resident petitions, the USCIS adjudicating officers are looking for potential for fraud, sham marriages, etc., and while age gap is not a disqualification, but is a red flag. So expect a more thorough questioning from the officers about the validity of the marriage. If everything is good and you are a genuine couple, there is nothing to worry.