There's plenty of room with 7 potential to make a U21 SF. Additional potential for that position is would actually be largely unnecessary to make the team. Webster made the team this season with 6 potential.
As for your question, tough, I can't give you a probability. Your guys has the base skills to reach the minimums required if you train him well, but I can't tell you what his competition would look like in season 25 for a roster spot. You'll just have to go for it and see