On one hand, a coach doesn’t want to keep a spot open for 2 years for an athlete he doesn’t know will stay in playing shape during those two years or even want to come to the school in 2 years. On the other hand, as they learned during covid, a 20 year old is two years bigger and stronger than an 18 year old and more mature in a lot of ways, with 4 years of eligibility remaining.
I think most coaches would be happy to have the older student as part of the team. They aren’t going to ‘hold’ the spot, but if the student keeps the coach informed of the timing to finish the mission and start school, the coach would be able to form that freshman recruiting team with this student on it. It might be a little different for a goalie or shot putter if another goalie or shot putter comes along, but for most sports with multiple players in a position, it should be fine.