These tomato plants have been growing inside and recently started to show spots. Is this mildew? Maybe growing to close together with no ventilation??

Welcome to NGA, @CRR98674 .

The spots on your tomato leaves don't appear to me to be mildew; maybe just a little damage from drying out a bit between waterings. The leaves do appear to be very pale to me though -- as though the plants aren't getting sufficient light. It appears that they are located in front of a window -- ? You might need to supplement the light with a fluorescent fixture or something similar if you won't be planting them out fairly soon.