Here is truth for NE HA D3's. If you are talking NESCAC, NEWMAC, type HA in New England. All velo's I talk about refer to RHP, lefties are just another thing.
Your kids situation is exactly my son's who is now at a really good school (I'm pretty tough about what I call HA) D3 in New England as a pitcher. He was a catcher but grew very tall and stayed very thin, and had a great slider so the HS coach told him he was a pitcher. He sat 79 Junior year and 80-81 senior year touching 83. Now sits 85 and touches 87+ in indoor bullpens, a bit better in games. D3 coaches want strike throwers and will actually pitch guys upper 70's if they throw strikes.
Your son's one knock may be he already has size (205lbs) compared to kids throwing his velo, is there 5mph in his mechanics, maybe, probably if he throws like a catcher, but the upside just by getting bigger is harder to see for a coach if the kids already over 200lbs. Unless that size is mush and not much muscle. Ask the coach or other knowledgeable baseball guys what his arm speed looks like. Unless he is severely under-throwing for his size because of mechanics, I'd be wary of gaining any more than 3-4mph in any year, too fast too soon is a recipe for injury. Velocity gain is also not linear, you can't count on the same gains each year.
People really over state velocity at all levels. Do you need to max 90 to get recruited at D1, yes, are the pitchers there all throwing that, no. D3 even most HA D3 the cutoff is about 78mph safer is 80mph.
Most teams my son's team played threw guys anywhere from 78 to 88mph, with an occasional 90mph arm but also the occasional 75mph arm, the majority sat 82-83. (that being said MIT has a kid who threw 96 in hs (injured), but in the weekend series they threw two guys in lower to mid 80's against my son's team)
RARELY, ACROSS MOST HA D3 DO KIDS PUMP OVER 90MPH IN GAME CONSISTENTLY. 88 IS FAST. DO THEY MAX OVER THAT, SURE, BUT THEY DONT' SIT IT AND THROW STRIKES. WHEN THEY DO AT D3, PEOPLE TAKE NOTICE AS ITS NOT AS COMMON AS MENTIONED. 83-85 throwing strikes gets you in the starting rotation and if you can either paint the outside corner or can spin the ball, you will have success.
People also like to talk about D3's as if only the top 25 ranked programs exist, most HA D3 are not top 25 and thus can't recruit top 25 D3 talent. Also most HA D3's are not MIT, Caltech or John Hopkins who can recruit world-wide based on the schools rep. if you are looking at those schools then I would say 83 isn't going to get you recruited there as a PO. As a multi-position player with the grades and potential to become a pitcher, maybe.
it's hard to get on the field as a catcher with 4 others on the team, but pitching is a commodity. It is hard making it as a catcher unless you can really hit, and I mean really hit. Being a multi-position guy is also key, IF YOU CAN HIT, the concept of the utility player for defense in D3 is non existent today. If your bat can get you on the field but not in front of the starting catcher, that's why you need to be able to play another position.
If he can be recruited in your opinion as a catcher, stick with that, because if he has the arm he can transition later, but I'd certainly let any coach know he pitches also.
IF he's not a great hitter, focus on pitching.