He's at it all the time now! If he's awake Alex wants to be vertical!
The best thing is holding him in the standing position and watching his smiles and giggles as he moves his head around.
He's also pushing himself over things (legs, pillows etc), which is quite cool.
I don't know what age kids are meant to be able to do certain things, but one of my pet peeves is when people say "My child is only X months old, but he's already performing at Y months." For me it's not about how advanced or whatever - it's about watching my son do things for the first time, and watching him learn.
Your kid might be able to play the piano at 7 weeks old, but I just watched Alex turn his head towrds me whilst I was supporting him...and then he grinned - and that's just about the best thing I've seen this week. :)