is possible with sex aruond ovulation day , Ovulation occurs 14 days prior to coming period.((21st day in 35 days cycle) If you have a35 days regular menstrual cycle, the sex on 29th day of cycle can not cause pregnancy.
If you had sen around 21st day OR if the cycle is more delayed-conception might have occured.
The doubt can be cleared with blood pregnancy test.
Before trying for ababy at the age of thirty five, one should get ovulation study done for having idea of ovulation day. A LH surge test can be used to determine ovulation in following months & plan for sex accordingly.