What size 2004 Start do you have?
There were 3 sizes in 2004...
Start x-small 150 235 85 56.0 13.0
Start small 180 255 100 67.7 14.2
Start large 210 265 110 71.8 15.5
With your weight at 210 lbs. (95.25 Kg.) I hope that you have the Start Large.
Your 25 kilometers/hr windspeed = 15.5 mph = 13.49 knots= mid Bft F4
If you have the Start Large (210 liters volume x 110 cm wide) you should be able to get planing in this windspeed with an 8.5 m2 sail.
I will ask the same question as James because there was no specific "packaged rig" that came with 2004 Starts. What size is your "stock sail". Also, what brand and model and what mast do you have?
Sailing on fresh water is not helping things due to less buoyancy, but a sailor your size should be able to get planing (with a good skill set) with a powerful 8.5 m2 rig on either the Start Large or the 180 liter Start S in about 14 kknots of wind.
Hope this helps,