For the benefit of the thread.....
Average frequency of sex per year:
- 18-29 years: 112
- 30-39 years: 86
- 40-49 years: 69
or (approximately) per month:
- 18-29 years: 9
- 30-39 years: 7
- 40-49 years: 6
Source: Piccinino, LJ, Mosher, WD.
Trends in contraceptive method use in the United States: 1982-1994. 1998. Family Planning Perspectives. Vol. 30(1): 4-10 & 6, Table 1.
The Kinsey Institute - Sexuality Information Links - FAQ [Related Resources]
This is just from one study, but I've seen similar numbers elsewhere.
Here you will find the yearly numbers ranging from 98 to 132, or 49 if you're single.