I think its good to be on safer side and try to have higher volume of coins so even if price doesn't reaches to the moon in future higher amount of coins will give us best benefits in future.
Actually the amount of bitcoins someone would need for getting retired later on would probably depend on the price of bitcoin of that time, if he has 50 bitcoin and the price is $10k it might be enough, or if he has 25 bitcoins and the price is $20k then it would also be enough as the value would be the same according to the price.
In 5 to 10 years, the bitcoin price will be around $10 to 50k. So you need about 100 bitcoin to live happily.