is 25 -26 too old for an international (Indian) student to pursue a Masters in Finance course from one of the universities in UK? Total Work Experience - 4 years . What is the job environment in UK for international students after finishing off the course?

Well said before, age does not play a role. It is irrelevant information. 26 is too old? What are going to say when you are 70?
Age could be a concern if you are about to reach pension age.
I am sorry to point out that in many places around where the work culture is different, opportunities are limited, competition is tough, people are judged by their age. Luckily this is not the case in the UK.