Maybe the answer is the old Roman method - nobody can enter into politics until they have reached a certain age and undergone certain experiences (in their case military service, in ours it would probably be having done a 'real' job). I'm not in favour of fixed terms because I believe it is beneficial for politicians to go on for as long as they like, using the benefit of their accumulated experience and wisdom, I just don't want them starting when they are barely out of university.