If you're born on the Digital Age and most of your life your expose to Internet, Mobile gaming, PS4 & Card games in School or at Home . Digital currencies will interest you rather than stocks. Digital currencies it still young and have a lot of room for growth Millenials do tend to like it more because of how active and volatile it is, similar to the fast phase that we are use to when we need to go to work and have quick breakfast.
I use to play Cabal an online Game where you have to venture and learn on your own on the digital world. Playing it taught me different things in real life, I bought a mythril set for 15000 PHP for me its worth it because for me it has value while playing the game. This holds true to digital gems, rare cards etc..
Younger people likes digital currency because they can appreciate and knows that even it is digital it can have values. This is something hard for older people to understand when you tell them that Bitcoins for example is worth 20000$.
To put it simply Bitcoin is powered by Math and algorithms - your money your bank. Unlike FIAT money that is centralize and hold by your BANK or STATE, which prove in times not that reliable because of TRUST.
