It's normal for people to make plans for retirement and before I got to know about crypto and Bitcoin investment, What was a normal routine for most business men that are self employed around me was to use their period of active service in building fleets of houses they would normally give out on rentals which after they're at the stage of retirement and are off the active service would serve to take care of all there upkeep till they grow old.
From what I've come to see, such investment has lots of disadvantages and limitations due to unforseen circumstances like war and government policies that could make the cite of the buildings inhabitable thereby making the investment unprofitable and sometimes most men at the point of retirements, discovering that they can't get access to all they've invested into become traumatized in the process.
I don't see any reason why you feel bitcoin is a better investment than owning a property which is also lucrative business, as you know bitcoin depends on electricity and any war could also really affect it to at least in some ares if the war is a major war and also government policies has been one major enemy of bitcoin.
The only reason why bitcoin would beat other form of investment is cause its a better store of value compared to fait, any other form of investment gives return of profits in fait and that seems to be a down side cause fajt continues to suffer inflation and the value of your returns would only get lower.
Investing into Bitcoin is good and for the time being, we can actually make a ten year speculation on the fact that it will still remain a valuable and profitable investment but the question here is;
I love the fact that you used the word speculation cause as you know anything can happen and bitcoin rise to the top was a major shock to people cause no-one actually believed in it when it started, but your right for now cause the facts available shows us that bitcoin could last even longer as more adoption takes place.
But it's also reasonable to have in mind that there is also a risk involved where you might lose all your investment and get no profit at all, which Is a possibility and also the opposite, and IMO I think it's wiser to actually make decisions based on possible senerio, therefore you should also consider diversifying your investment Portfolio into other assets like having a major shares in a company, stock and bonds or even something as tangible as real estate, I'd you really are planning for retirement then I think you don't want to get disappointed if bitcoin fails you, so this is also a better option than having only one asset in hand.
Is it wise and realistic for someone in his early twenties to set up Bitcoin as a retirement plan such that he continues accumulating Bitcoin from this time till he gets to his retirement age?
To me it depends cause I've hardly seen any person at his youth that is balances enough to start planning for retirement unless he plans on retiring early, I have a friend that wants to retire at 30-35 and yes he could plan ahead with investment a major part if his savings in bitcoin and other asset.
Most youths would invest for their dreams, like lifestyle and to get to a better level of life. So yes It is wise and a good idea to, there is nothing wrong with investment little amount of cash for retirement.