Which contact lens to choose

One often wonders:

1) What is the right age for taking to contact lenses?
2) Are contact lenses safe?
3) Can I wear contact lenses after 40 yrs. of age?
4) Is it right for a teenager to take to contact lenses?
5) Which lens should I choose for my eyes?
6) Can I wear lenses during sports or for long hours?

and many more such queries often bother us. Please post all your queries and I shall be glad to answer them