Hi. Either she is peeing from excitement or because she is being submissive. From now on, ignore her when she is in an excitable state, when she is calm, say hello to her outside, on the grass, so that if she makes a mistake its not such a problem. She could also be nervous, have you shouted at her or smacked her for weeing when you she should not? If she does wee when you say hello to her, just ignore the wee. And yes, most definately, you can train any dog of any age...7 months is a great age to do training.
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