Doc Christopher's dosage formula is still the best I know of and I use it 
exclusively all the time.  
 
It's called the 150 rule.  
 
Take a person's weight and put that figure over 150.  Reduce the resultant 
fraction down to its smallest common denominator and you have your dosage.  
 
I never go by age as that is too uncertain.  You may have a six month old who 
weighs 15 lbs or 30 lbs depending on genetic makeup, health, etc.  I would give 
these two babies totally different dosages though I might start both on just 
one drop of a tincture.  
 
Using the above rule, it would work out this way:
Baby #1 @ 15 lbs would get this dosage.  15/150 reduces to 1/10th the normal dosage.
Baby #2 @ 30 lbs would get this dosage.  30/150 reduces to 1/5th the normal dosage.
 
When it comes to babies and the elderly who are really sick, I will test "one 
drop" on the patients tongue to see if there is any adverse reaction first, and 
if none, will work up to the above formula dosages usually within the first 
day, always monitoring as I go along and increasing the dosage.  I've given 
Cayenne to very young children starting with drops and ending with dropperfuls 
to tremendous results.  
 
Hope this helps.
 
Love,
 
Ian "Doc" Shillington