When should I invite him to my birthday dinner?

My boyfriend and I have just recently entered our relationship. We have known each other and been friends for a few months now. My dad just asked if I would be inviting him to my birthday dinner, which is 5 months from now. Said dinner is only close family - mom dad, sister and her boyfriend, aunt and uncle. I wanted to know how long I should wait to invite him.
When should I invite him to my birthday dinner?
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