I followed the instructions of Arden with the correction from @YInui and just wanted to share my experience…
So one thing to note is apparently we just get 5 calculation properties. Just for this to work I had to use 2. So we’re up to 4 out of 5 being used. Kind of annoying to see the little note that’s like “you’re using 4/5, talk to sales” when really they just should be fixing it themselves. But I digress.
So we already had a DOB property. Then I created the property “internal - last date age calculated”. And I created an active contact list with these filter criteria:
Basically, it means that the ages for our activie clients will be within 2 days of correct and the ages for people in our database who aren’t our active clients will be within a month of being correct. That was my compromise.
Then I created the workflow described, so once someone was added to that list, the “internal - last date age calculated” date gets updated to the date this action is happening (re-enrollment allowed).
Next I created the calculation property “internal - calculated age (rounded)”. This part was a bit tricky. So you create a new contact property. Click next and field type is calculation. Then “build calculation” and in “calculated property type” you need to change it from “custom equation” to “time between”. I didn’t quite understand that from the above directions so I had to call Hubspot for help. Once I did that, then I was able to find DOB and “internal - last date age calculated” to make that property work.
Then I did that second calculation property described (Calculated Age) and used the 31,536 number but when I tested it, I found that the calculation was wrong. Someone who was 83.9 something was showing as over 84. So then I changed the number to the 31,557,600,000 listed by @YInui and I believe my Calculated Age is fairly accurate now!
I hope this helps. Anyone that needs this, I encourage you to one, upvote this original question and 2, call support to get help doing this work around, then they’ll start to see how many people need this and one day maybe they’ll fix it!