No I do not think that youngsters or anyone should go all in on bitcoin because firstly it's prices keeps on fluctuating which means that if there is a chance of increase there is equal chances of decrease in value. Secondly it is not centralised form of currency which means it's not regulated by any government or bank so it's not a good option to go all in with it.
Fluctuation in price should not stop anyone including youngsters in investing in bitcoin if they wish. With no responsibilities, I guess it is even the best time for them.
Every youngster should learn how to save, and bitcoin has actually provided an avenue and an incentive for everyone to learn how to save. Youngsters should be encouraged and not discouraged as it is their future. However, they could still diversify a bit if there are other options.