In all honesty one of the most exciting things as a parent is watching their youngster get hooked on their "thing". Doesn't matter what it is, just seeing the passion for something come out at a young age makes a Dad's heart proud!!! It's obvious you are enjoying this moment and are proud, as you should be.
I think in our times something like this becomes rarer, not sure why. After a few false starts in other things, we had a son get hooked on photography at a young age, it's now his work and he's loving it.
I may be biased, but I think fishing is a fine passion and tying flies will get a young man through many a cold winter.