Finding someone who would "mentor" you would be a challenge, I expect. All coin dealers are struggling, they do not need to create extra competition for themselves by helping another coin dealer start up. And most aren't big enough to afford to hire assistants, which is the only way someone could actually gain real-world experience in coin dealing.
"Brick and mortar" coin dealers were struggling with the competition from the Internet even before COVID; COVID lockdowns forced everybody to either close up shop completely or go online, and most folks who hadn't tried the online thing before have now realised how much less hassle it is. Many shops that closed during COVID are not re-opening.
Here are some challenges to being a successful B&M coin dealer.
You need to be a "people person". People won't want to sell you their coins, or buy from you, if they don't trust you, and it's much easier to trust someone that you actually like.
At the same time, you need to be a hard-nosed business person. You need to make a profit to pay your bills and buy in new stock, and that means you need to buy low, and sell high. I know one person who was a coin dealer for years; he was an ex-collector and very knowledgeable about coins, but he wasn't as successful in the business as he could have been, because everybody who came into his store with a sad story about how these are coins from grandma who's just passed away, or they've got to sell off their coin collection to pay for lifesaving cancer surgery, or whatever, he would pay them extra for their coins because he felt sorry for them. "Feelings" are very human, but also very anti-capitalistic. I realise that this second point can directly contradict what I said in the first point; you have to work out how to strike that balance.
Likewise, as noted above, and just like people who "invest" in rare coins, "sentimentality" about your own stock can get in the way of profitability, and thus whether you can stay in business or not. I know that some coin dealers remain coin collectors and routinely "buy their own stock" for their personal collections, but only the richest and most successful dealers can afford to do this as much as they might like to. You might really, really like this coin or that coin, but if a customer comes in and likes it too, you've got to sell it, and got to be keen and enthusiastic about selling it.
You have to be prepared for the discouragements. Can you tell someone, to their face, that grandma's expensive coin collection is worthless because she polished the coins to death? Or that the 1970s plastic coin album they've kept their coins in since they were a kid, has ruined the coins? Or that those expensive Franklin Mint coin sets their great aunt bought for them in the 1980s are now worthless because the packaging has decomposed and destroyed the coins? Or that the ancient coins they bought on a cruise to Greece and Turkey are actually fake? Or how about the person who insists that grandpa's coins must be worth a fortune, and says you're lying and trying to rip them off by not paying a fortune for them?
Then there's the "mercenary majority" angle. Several of the coin dealers that I visit regularly, have told me that I'm just about the only "real coin collector" they regularly see; practically everyone else who walks in the door just wants to buy and sell bullion, or to flip the latest Mint products, or whatever. Meanwhile, their awesome inventory of amazing coins just sits there, unlooked-at by all but the tiny minority of their customers.
No wonder most B&M coin dealers still sell most of their stock online.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis