Do all your buildings need to be at level 20 to upgrade to SH 22?
Strong hold 21 ONLY per say, BUT you will need iron WAY PAST level 20 only. But the houses and mines and like that do NOT have to be
SH currently at 21 mines at 20 one at advanced lvl 2, all iron storage at 20
click on your iron supply and it will tell you the max. If its not enough then you will have to get the advanced iron up more
All iron storages @ 20 and advanced @ 5 for 22 and @ 10 for 23