When you say 35 it would be strange for it to be anything but years.

3 days, weeks, months or years are ironically all common units when someone is "3".

No one actually says "my child is 3" meaning anything other than 3 years. They would say "3 days", "3 weeks" or "3 months" meaning the other lengths of time.

Not where I live. You'd never specify how old somebody is with a bare number and have it mean anything other than years in the US. "My kid is 3" is always 3 years. So is "How old is your Tammy?" "Three". That only ever means years. Every other unit is always explicit. In my decades as a parent and being around other parents of kids and newborns, I've never experienced an exception to this.

Most of the time if someone says "he's 3", it is a good bet that they mean 3 years. People usually specify if they mean days/weeks/months with respect to someone's age. Not always, of course, but it's definitely uncommon to drop the unit when it's anything except years.