Late Afternoon wedding guest attire?

I've got a bit of a tricky wedding coming up. It's summer, outdoors, with an indoor reception to follow immediately. It starts at 4:30, so the reception is going to be evening. I'm also pretty young, so even summer suits are age inappropriate. Can anyone help me out here?
Update: I've got a bit of a tricky wedding coming up. It's summer, outdoors, with an indoor reception to follow immediately. It starts at 4:30, so the reception is going to be evening. I'm also pretty young, so even summer suits are age inappropriate. Can anyone help me out here? EDIT: I should add,... show more I've got a bit of a tricky wedding coming up. It's summer, outdoors, with an indoor reception to follow immediately. It starts at 4:30, so the reception is going to be evening. I'm also pretty young, so even summer suits are age inappropriate. Can anyone help me out here?

EDIT:

I should add, I'm a guest, not the bride.
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