Well, there are individuals who stand out (Mozart, Schubert) who had composed symphonies (but not for the whole orchestra) when they were at a young age (15-21?) as we know it. For the past 70 years, nothing noteworthy is coming along and from my philosophical point of view, people are getting "distracted" and more lazier. It's certainly not norm to compose symphonies nowadays (I am distracted by this) at a young age but they do compose other works such as chamber music...
The main plan is to get this symphony done so I can start working on small scale instrumentation such as chamber music as I have noted and quartets etc...