* If your phone is loaded with junk and cache files, slowing down is certain. In general, android devices have a cache partition which can be clogged by junk files. If the partition is full, then the operating system and the apps start working slow.
* You may not love this but weathered damage can also make your phone run slow. Either it could be an incident where your phone became wet in water or it would be a strong all on the ground which is not fatal though.
* The heat or the temperature, high in numbers could lead to slowness in working pattern. Heat lowers the frequency of performance in smartphones. This is the reason why you feel phone getting slowed down with heavy games.
* Operate your phones on custom ROM, or default ROM. User who generally have this itch of trying new things download third party ROM from internet. This might lead to slow performance as there is no guarantee of non custom ROM mingling with your smartphone.