I am running Linux Mint on my old netbook and it really consumes a lot of power. If I install Android, will it actually consume less power? I actually want to use the same device for at least 2-3 hours whereas on Linux Mint, it only works for 1.2 hours. Is Android suited for such a use?
While there is an Android port for x86-based devices -- that is, regular PCs -- I'm not sure if it is ready for normal use yet. Even if it is, you won't get that large an improvement of battery life: Android may be optimized for using little power but desktop Linux has the most important power management features, e.g. CPU scaling, as well.
But 1.2 hours of battery life is really bad for a netbook. Since it's an old one the battery might be worn out. In this case you'll have to replace it but a compatible new one top get decent battery life again.
Before you go and spend money on a new battery you might want to make sure that management does actually work on you computer. You should find help on how to do this in your distribution's or a general Linux support forum, or possibly on superuser.