My blood pressure is 105/70. is that too low? when would blood pressure be too low?

That is an optimal blood pressure at your age. The blood pressure is low when the tissue perfusion of the important organs such as brain and kidneys are impaired, and that happens when the mean arterial pressure (MAP) is less than 65 (MAP = systolic pressure plus 2 times of diastolic pressure divided by 3), e.g. BP of 90/50 is low for an adult because MAP is less than 65.

When developing symptoms attributable to low blood pressure. Your blood pressure appears in the normal range otherwise.

Your blood pressure not only normal it is a good reading. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV, Flu and Covid vaccines. Wish you good health!