Didn't read his blog but his goals are unreachable in his two-year time frame>Make a blog that will inspire other people to reach their goals as well
This is the only one you can realistically help him with. Shoot him a mail saying you've read his blog and it gave you resolve to improve yourself and whatnot>Reach 30.000 subscribers on youtube
Does he create content ? If so, you might share a couple vids of his to mates of yours that may be interested, that could help him
But 30.000 sounds like a lot>Become fluent in japanese
Very difficult to do in this little time, unless being a "full-stack dev" is being one of these clueless wankers who think they know how to code when they don't understand a bloody thing about the internals of their beloved frameworks.
Again, nothing you can do will help>Build a web application that will encourage people to learn japanese
Straight up impossible. Doing that alone in two years would be extremely time-consuming even for an experienced dev, a newbie has no chance.
If you have development experience you may be able to help >Commit to the gym
Possible but that would divert time away from his other, already unfulfillable ambitions. I guess only IRL friends could help him with that>Get my driving license
Easy but probably time-consuming as well. You can't help on this one either.>Read 50 books
That's a book every two weeks. Unless you're reading literal children tales there's no way you can read that much AND sustain the other stuff. Reading is personal, so again, no help possible>Publish a book
I have no experience in book-writing but my gut feeling is that, again, two years simply isn't enough to even write the bloody thing
If you really want to help him, tell him he needs to focus his attention on one project at a time, and that doing things well require a lot of time.