I think that 60 cm is standard. I don’t know why, but Germans usually have a pretty good reason for whatever they are doing, and especially when it concerns standardization of something.
I have seen older ones that are a bit longer, say maybe 70 cm, but I have never tried any of those.
In my opinion 60 cm is really fine for a jointer. But if you want to try a longer plane I see no reason why not.
Here is one that is 66 cm long http://www.ebay.de/itm/alter-seltener-Hobel-Rauhbank-/400996840391?hash=item5d5d4633c7
Here is one that is 65 cm long http://www.ebay.de/itm/alter-seltener-Hobel-Rauhbank-/400996325333?hash=item5d5d3e57d5
Here is another one of 66 cm length http://www.ebay.de/itm/antiker-Hobel-Schreiner-Zimmermann-Werkzeug-Rauhbank-Langhobel-Holz-5-1cm-Klinge-/360844052435?hash=item5403fb47d3
I’ll check when I get home (I am at work in Norway at present)