My female dog has gone into heat for the first time. She doesn't seem to be acting any differntly except for when she'll be laying down && my older male dog who is fixed, will come && smell her, she'll go crazy && try to bite him. But if she's up, she'll play fine with him like normal. Is this normal?

It was normal with my dogs. Dogs have moods too.
Make sure no stray non-fixed dog starts sniffing around cause once it jumps on her it is impossible to get them apart.

Keep the fixed male away from her too. He may still mate with her injuring or infecting her. Be extreamly careful in another week . Don't underestimate what she and any male will do get together. As she gets into the third week, she will become more and more desperate to get loose.

Get her spayed as soon as a vet will do it.