The original post was about the United States . I admit knowing nothing about France or Belgium laws. I hope it is still good for you in the future. Here I would never try it myself after my old American born wife's money grab. They can take everything away here very easily.
If you are going to be in a relationship with someone who you are bringing to the United States that person yes 10 years age difference max. I would say 2 years or less probably best IMO. You want someone who will be if similar values and life history. I have a Phillipean woman friend here in the United States. She said knows a few Phillipean women married to older guys with young guys on the side. You are going to want an actual freind in life not a girl who could be your kids age with power over that person. It ain't going to work in the West.