US Immigration from Uruguay

Is anyone facing delays in the approval of the I-829 (removal of condition on Investor immigrant EB-5)

I am a US citizen over 21 years of age. Can I petition my sibling (who is currently 15 years old) via I-130? I know it's faster if my parents immigrate but they are not interested in doing so. I realize my sibling will have to wait 10+ years and I'm fine with that. I'm just wondering if he has to be of a certain age for me to be able to file a I-130 on his behalf? Also, must he remain unmarried the entire waiting period?

My step son has a valid PR status. In Oct 2019 he went to uruguay with the intention of returning to the USA within 6 months. Due to fears of travel during covid, he has been delaying travel and now its been a year and a month. He has a ticket for this weekend to return, will they deny him entry to the USA? Normally after a year you would need to get a new visa but are they being at all flexible due to the covid pandemic? If they do refuse him entry, what happens?

Since I'm aware you have to have 40 Credit to Earn the Social Security pay when you retire, but how would that applies to Immigrant that doesn't have 40 earned credits? Do they need to submit any at all?