Old and Grey

How do you explain "old" to a 3 year old.

I was trying to tell Molly-Mae that Hurricane is getting old because his fur was turning grey around his mouth. She said "What is old mummy".

Me - "Everyone turns old at some point, you're getting older, you're nearly 4"
MM - "But I don't want to get old mummy"
Me - "Well we can't do anything about it, as each day passes we all get a little older and when you're old like Hurricane and I we start to get grey hair"
MM - "I want to see your grey hair"

I pull my hair apart to show her my grey roots and she said,

"It's ok mummy, I'll just blow the grey away" and she started to blow on my hair.

If only it could be that simple!