How to explain to kid that i was 60 when born?

Truth: Not sure what you're exactly asking here, but straight truth works best. I'm assuming you're dad, and the child's mother is much younger. It won't take long for them to do the math, and you'll look the age, so just come clean. Small children don't care, and older ones will know you're lying.

Depends on the kid: Kids over 15-18 can be told as you would any adult. They have most of the processing capabilities of an adult. For the 8 to 12 crowd, straightforward with no elaboration unless asked.They are at a very concrete thinking stage.Under 8 or so you do short and sweet. No lengthy explanations or discussions. With these you expect to get occasional questions on the issue for months to years.