The lack of show record at that age will be the hurdle, because the show record is evidence that the 20 year old can still handle the rigors of training and showing. And even if you explain that the lack of a record was due to you and not him, putting a 20 y.o. back into training & showing after years of light work is still a gamble. You can’t know that he will hold up to the increased workload and all the variables that come with travelling and showing, and you’ll quickly spend a large percentage of his (potential) value just getting him back into the ring.
Leasing, while not what you really want to do, is probably the best answer. Two years of lease fees will net more cash than what you’re likely to get right now. At that point you’ve recouped enough that you can sell cheap to the bestest home that offers up a check. And if he really is a star, he’ll have a line of people ready to pick up his tab each year. Even 3 years at a very cheap 10k/yr would be a great return when compared to what you have standing in the field.
Or lease to purchase, so buyer can get him back in the ring and confirm he’ll hold up without the commitment. But flat out purchase, without spending the $$$$ to reestablish his show record, is a tough sell. People shopping that ~20k market just can’t afford to throw that cash away with a risky purchase that might wash up in 6 months.