Can military or police service be made mandatory in India for young people?

As of now, it is not. And the simple reason for that is - our huge population.

That has always ensured that there are enough volunteers to enrol themselves, every time vacancies come up. In fact, ditto for China (PRC) as well. Hence no need is felt to make anything really 'compulsory'. Hence, no rigid conscription.

But it's a great idea and can help India in several ways.

1. Dignity of labour - Most young women and men (18 yrs +) hardly understand the value of manual labour, or any labour for that matter. Getting educated formally, and landing a cushy job is all that's aimed for. It will change in a big way. Young ones will become far more sensible.
2. Pride for the nation - Almost instantly, there will be a change in perspective for most. Their approach may undergo a radical overhaul.