About 6 months is the average age of sexual maturity for chickens. Males can possibly breed earlier and Silkies tend to fully mature a little later, but that's about average. If you aren't in a hurry, I'd wait until 7 or 8 months to incubate any eggs. Also, remember that Silkies have fluffy butts that impede contact, you may have to trim the feathers a little to make sure they get a good connection.
Roosters crow for many reasons, one of which is competition. Each one was trying to outdo the other to show that they were the top rooster and determine flock hierarchy. Without hearing another rooster the one you have may not feel the need to show off as much. Silkies tend not to crow quite as much as some other breeds, but he will probably crow more as he gets older and more sexually mature.