Should I up to a 30 gallon?

[Neal]

I bought my male BP at 30 inches and the guy at the reptile show suggested I use a 20 gallon. He's 32 inches now. Is it too soon for a 30? My sister needs a 20 for her new turtle so I was thinking I should just up and give her the 20

You can but you don't need to. Some things to consider are that with a larger tank comes the issues of keeping the heat gradient ideal. A 30 gal would be fine, but you'd have to do some serious crowding as to make it seem tight fitting.