Hi Jam,
Minimum age is 19. No upper age restrictions any more. This is now illegal - so Virgin has had to drop it.
Age of the crew really varies, from what I see myself I estimate the average age of a new joiner is early twenties, though you do see some 19 / 20 year olds joining, and also some in their 30's, 40's and even 50's.
We did an average age competition on a recent MCO I operated, and the answer was 29. Though this figure included 3 ancient wrinkly old flight deck.
I don’t believe there are any male cabin crew of Indian origin at the London base, though there are a few Indian origin females. In any case, regardless of whether there are or aren’t, you would be more than welcome as there is no difference at all. Crew from Virgin come from all walks of life and all backgrounds, and everyone (usually) gets on very well!
Virgin has bases in Delhi and Mumbai where all the crew are Indian nationals.
Hope this info helps!