You must not play tennis.または
Don't play tennis.

You have not to run fast.

shall we play tennis?－yes,lets.

shall I sing?yes, please.

this bag is smaller than that one.

this bag is the smallest of three.

jyon is as old as ken.

this book is more difficult than that one.

this book is the most difficult of four.

Be kind to elderly people.(old people )
↑old よりも、elderly の方が失礼のない言い方