when? it depends on how you define "alt season"!

for most people who have been around the altcoin season is every day that a shitcoin gets pumped and they can make a profit from that pump. and it is happening almost every day and traders are taking advantage.

for some others who don't have any experience in trading altcoins, the alt season is when they can close their eyes, choose anything at random and make profit!!! that case is the rarest thing you can ever hope for. so it may never repeat or it may happen in another 10 years.