Thanks for asking Stacey.
The modern IQ tests don't use 'mental age' anymore - they use 'unusualness of IQ level' to give a score.
(person A who has an IQ of 120 is not 'twice as smart' as person B with IQ 60)
Rather, a score of 100 is the most common score, scores at 130 or higher are rarer, with only about 3% of the population scoring 130 or higher.
Hope that helps!
As for as estimating - I would look to who your child likes to socialize with for a 'social age' what they like to learn for an 'academic age' and how they navigate the world for an 'executive function age.' I wouldn't look at the scores, I'd look at the child's behavior.
Smiles,
Grinity
