Fourth house is the house of shelter. Ketu is recluse and hates the portfolios of fourth house. But with Ketu in fourth house there would be Rahu in tenth house as Rahu is always 180 degrees away from Ketu. Most influential politicians have Rahu in tenth house like Donald Trump, M. K Gandhi and many others. So Ketu in fourth house isn't bad in the second half of life atleast. 

     In the first half of life Ketu is a bothersome planet in fourth house. Fourth house rules over mother and basic education. Mother could be caring but unable to truly understand the native. Ketu in fourth house generally means less grades or failures in school and college education. Unless there are other planets which benefit education this scenario holds true. Fourth house also rules over motherland and shelter. Ketu prefers being alone and dislikes comfort and shelter of home. A person remains restless at home due to Ketu in fourth house. 

    Fourth house also rules over heart and old age. There are chances of heart surgery if other malefics are associated with Ketu. There can be problems and troubles harassing a person in old age. But as someone rightly said: "Opportunities often come disguised as obstacles". By the time of old age native has already had his fair share of troubles and learned from them. With Rahu in tenth house its likely that youth years would also show troubles and native learns from them and becomes a successful person in old age. 

     Ketu in fourth house is a tale of two halves. First half is generally a bad experience unless other planets help. Native learns from failures and in the second half becomes a success despite of troubles.