New and dealing with early onset

Welcome to the forum, though I am so sorry you are facing this. Educate yourself about anosognosia: this is a common feature of dementia, it's different from denial, it prevents him from perceiving his deficits and so he thinks he's fine. Most people with dementia are this way: he'll probably never acknowledge that he has it.

In the past, it didn't make much of a difference if you went through all the diagnostic steps, because there was no treatment; some people need a diagnosis to qualify for disability though, and that may affect your husband, since you said he's not working. Now, things are changing on the treatment front too, and possible treatments might be a reason to try to convince him to go. The new amyloid treatments (Leqembi is the most recent) are effective in Caucasian men if started early, and he might be a candidate. That said, it's still not easy: administered by IV infusion every two weeks over 18 months, out of pocket cost around $25,000 per year, and the studies showed delay of deterioration of about six months. Long haul for a short slide, honestly, but it's probably worth discussing with a knowledgeable physician.

If you look to the right under Quick Links and Groups, there is one for new members with a lot of useful information, including a staging tool that may give you a clue how far along he is.

If you haven't done it already, address legal and financial issues as soon as possible. You need to have durable power of attorney for healthcare and finances, and you need to think about how you might finance care: if you're still working, you may need a day program, in-home help, and memory care at some point. You may need to structure your assets so that he will be eligible for Medicaid. Talk to a certified elder law attorney if you haven't done these things already (look at nelf.org for lists by location).

You have come to a good place for advice and support. There are lots of us here in the same boat. If you read a lot of threads, you will learn a lot and feel less alone, for sure.

I think M1 covered it, not much more to say other than hang in there because it can be a long difficult road, mostly for yourself as you will be the caregiver.
Possibly though you should convince him to get tested because it could be due to something treatable, probably not likely but without testing one never knows. Sounds like he is in good health otherwise so there is nothing to lose but if the tests are negative for a treatable disease then that also would answer the question as well. Might be a tough ask. Sorry you are here but there are a lot of smart folks here, not including myself.