[u]First Stage[/u]
Anywhere Sex-Mostly newlyweds experience this. Sex is initiated just about anywhere.

[u]Second Stage[/u]
Bedroom Sex-For different reasons (kids, visiting relatives, etc.), sex is almost always in the bedroom. More familiar area, more intimate, private, etc.

[u]Third Stage[/u]
Hallway Sex-Is where you walk by each other in the hallway of the house and give each other the "look" and you both go, "Fuck You!"

I always thought the three stages were:

Age 20-40  Tri-Weekly

Age 20-60  Try Weekly

Age 60+    Try Weakly