I understand that it's very important to start your investment journey very early, at a young age which is an added advantage, but putting the exact amount they should be investing is what I didn't find ideal, because everyone don't have the same financial capacity, the way $10 might be very little for you, might be a very huge amount of money for some young lads out there, the best thing is for them to cut their coat according to their size, by investing what they can afford to do away with for a very long period of time, and we all know our level better than anyone else, so it's best to act according to our level financially.
But one thing am quite certain of is that if they can be very consistent in their accumulation, in ten years time or more, no matter how small they invest weekly or monthly, they would have accumulated a very good stash of Bitcoin if they are consistent in their accumulation.
It is good to start investing early but it is also good to think about how much money each person has. Saying that people should invest certain amount of money is not realistic and can be discouraging for those who do not have lot of money. Your idea to cut their coat according to their size is smart because it reminds people to only invest what they can afford and to think about their long term financial goals. With doing this people can make smart decisions that fit their own financial situations and goals.
Three's no specific time to invest for Bitcoin especially for a long term investor, if you are just realizing the importance of investing in Bitcoin start the very moment you realized yourself and for the amount that comes into your hands, you mustn't start with the amount some else suggested to you that's wrong, start with an amount that you can keep up with and keep increasing your purchasing capital the more you make more progress in your finances but do not wait until you get a certain amount of money before you start your investment journey you will end up procrastinating and not making any good move. The idea of cut your coat according to your size only comes in when you what to invest more than amount you can afford, for instance if you make $100 I don't expect you to invest everything because you will be affected if you don't have anything to use to sustain yourself or your family that's why you are encouraged to invest with an amount that won't affect your finances like other things you do like taking care of yourself and paying for house bills.