30GB. It’s not so much about the space. It’s the baggage of having access to a ton of information. And the increased risk of losing my identity of my account was hacked.
If you're worried about your email history getting hacked, download the email instead and store it offline. It can be very useful to have a complete history you can search, but that doesn't mean you have to be keep it on a server. (Desktop clients are a great thing.)
Which is more sensitive if your account is hacked? Emails from 20 years ago, or emails from this past month?
Flip a coin. I probably have some emails from 20 years ago that contain health information, SSNs, passport info, etc.