CS/ICWA

1.  There is no age limit for CS/CWA.  Hence you can appear for the courses as and when you want. CS takes lesser time to complete than CWA due to difference in articleship period. 

You will have to put extra efforts and hard work as you are not from commerce background suitable for these two fields(assuming you have done graduation in same field)

2.  Regarding Age & Job prospect combination it may differ from case to case, but still if you have good command and knowledge in your field, i think it will help you in getting good job opportunities.

3.  Your third question can be better answered by you.  You can start your own practise if you think you can afford some more years as generally practise in any field takes some time to establish properly.  Its a subjective decision.

there is no age limit for studys you can do.....