Age description and hyphenating

How would I say a toddler is 2 years and 7 months old correctly? Is this right:

It is a two-year-seven-month-old toddler.

Or do I need an “and” between? I personally think hyphenating here looks ridiculous. In formal English, say a report document about child behaviour or whatever, could I write

It is a two year, seven month old toddler

instead, too?

Solution 1:

I have never actually seen either of those usages; what I normally see is either

thirty-one-month-old [child]

or, if less precision is needed,

two-and-a-half-year-old [child]

You could also say

[S/he] is two years and seven months old

or

[S/he] is thirty-one months old