I have 37 years experience as an immigration lawyer.
Oh, I wish could say an age gap of several years has no impact on a spousal or fiance petition but it is one of the flags.
The other flag I saw before even getting to the end of your question is Nigeria.
Any, and I mean any petition, involving a citizen of Nigeria marrying or being engaged to a US citizen is automatically suspect and scrutinized.
Further, you are asking for a waiver of a personal meeting. That is another stumbling block in this immigration matter.
If you wish to proceed, you without a doubt need to retain an attorney experienced in fiance visa petitions and have them prepare a detailed Memorandum requesting your waiver well documented with your medical evidence. The Memorandum should also be on the offensive explaining your reasons for wanting to marry the younger man and what he finds appealing with a woman 70 years old. I am not being disrespectful, I am 69 and also had back fusion surgery so I totally understand where you are at. Just keep in mind that the ones reviewing your petition are not in our shoes and are young 30 something. Like myself, they probably don't believe one gets beyond 50. So you have the burden of explaining your relationship and grounds for the waiver.
I just want you to know that waivers are rarely granted and I have had cases of paraplegic being refused the personal meeting waiver. It is discretionary.
That being said, if this is your only and last true love, then you probably don't have any choice but to give it your best and pray that you have a reasonable and compassionate examiner and that your petition is approved.
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