For character ages, you should write it as BOB, 35, or BOB, (35),. I personally don't use the parens as it is falling out of style.
In the script, whether action or dialog, you should spell out numbers up to three words, like one hundred and ten.
But four or more words, use numbers, like 1345 (which if spelled out to "one thousand and fourty five" would be hard on the eyes.)
The exception to this is a number which we are used to seeing in a certain form. Adresses, for instance, I would use numbers only, since that is what we are used to seeing on envelopes all our lives.
Now of course this is my personal way of doing things, I have found scripts that show different ways of doing it, so you decide what's best for you.