Is it safe to use 60W MagSafe 1st gen with Air

My brother has a MacBook Air wich uses a 45W MagSafe 2 charger, which broke last week. I have two chargers, both 60W for my MacBook Pro. He's using my older one which is a 60W MagSafe 1 and it has an adaptor so it can be used with the MagSafe 2. Is it safe to use this charger until it's replaced? I know if you use an iPad charger for an iPhone, it will ruin the battery over time. I'm just curious if it would have the same effect?