my little girl is 18 months now, running around and repeating stuff she hears... I'm not sure if she'd get bored at a match, but she's still too young, even though she knows what "kick the ball" means and she does it herself with her mini-football that I bought her!
at 5 months (?) if I read your posting right, you've got a baby who might not even be able to sit up straight without support; my suggestion would be to wait until both of you could get more out of it... at that age you may end up with a distressed infant on your hands and not be able to do much about it when inside the ground. I would strongly urge you to have her watch her footie on the television for the moment, and see how long she can deal with that before plunging her and yourself into the real thing... it might not be a good idea unless your 5 month-old is actually going 5 years old.