Historically, there are many examples of formerly left-wing/liberal politicians, theorists or activists turning conservative while ageing. Strangely enough, I can't think of many examples where it is the other way around: conservatives who later reject some of their views and adopt attitudes that are generally considered to be more liberal. Coming into my mind are:
Martin Niemöller - staunchly nationalist free corps member in the years following WW1, who later became a pacifist and was among the religious opposition to Hitler during National Socialism; after the way, still a pacifist campaigner.
Mir-Hossein Mousavi - Although considered to be one of the leftists of the regime, he was originally part of the establishment of the Islamic Republic of Iran. In 2009, he became a hero of the younger generation of protesters and was in favour of democratisation and liberalisation, therefore turning into an anti-establishment figure.
Any other ideas? Possibly Barry Goldwater?