But is this really an ideal idea?
many use bitcoin as their retirement plan because unlike just saving money your money will grow since bitcoin is anti-inflation its value will not decrease over time compared to fiat where not spending it will not be beneficial so if you want to “save” money for the future hold it in bitcoin
But bitcoin is a highly volatile asset and investing in it is risky, it can increase the value of your money but it can also decrease the value of your money. There is no guarantee that in 20 or 30 years, bitcoin will still exist or still have value. So using bitcoin for retirement planning is a good idea but putting all your money into a single asset is a bad idea.
I agree with what icalical said: we should diversify with more stable and safe assets like gold, bonds or real estate and some savings, don't just focus solely on bitcoin or any asset.