I will offer two different perspectives on how this could/should be handled:
Option 1 - If and I mean only if your own policy has some type of endorsement that requires replacement cost if your vehicle is wrecked in the first 12 months, then I would argue the hassle with dealing with a third/claimant carrier may not be worth it. Your insurance company can replace the car and subrogate the other carrier. With that being said, it is not guaranteed depending on state precedent that your carrier will be reimbursed in full due to technically only owing ACV. This would leave some type of balance paid to you by your carrier which if frequency becomes an issue could without being known to you be used against you in non-renewing.
I would recommend using this option if the other carrier is acting difficult or stalling. Keep in mind while it was the old man's fault his carrier is under no form of contractural obligation to pay you. This could leave you with outstanding towing/storage fees that need to be mitigated when handling this matter.
Option 2 - I think OP has every right legally to ask for true replacement value on his vehicle bc of how new it is. Again with that being said a minimal amount of depreciation may be taken as he has driven the car 5k miles. If you are not presenting an injury claim, then I feel like for such extreme damage a fair procedure would be to just replace it.
Now the not so fun part starts, all carriers have different views about fully indemnifying insureds and claimants. Depending on who the carrier is could go to great lengths in determining if they will pay or stall. This is the unfortunate part of the industry. I would remain calm and present this to the adjuster, all carriers like to prevent litigation at all costs so most of the time if your demand is reasonable, which in this case for a $40-50k car I think is, then they should handle it as such.
The one thing to keep in mind is when dealing with the third part carrier, remember they don't owe you anything and are just fine with letting this drag out which usually becomes more expensive for all those involved. Legal council is not a bad option of your aren't a good negotiator, but unless bodily injury is involved most won't waste their time with just property damage.
Let me know if I can assist with anything else or anyone has any questions.