If you want a better chance of success you will dump the OLD soil out and replace it with POTTING SOIL. Do not use garden soil. Do not put rock or gravel below the soil and above the drainage hole. Raise the bottom of the pot off any surface to improve drainage. Potting soil is cheap. Garden soil does not belong in pots unless you ABSOLUTELY are unable to get potting soil because you live in the middle of Alaska with no Home Depot or Grocery store. Or India I have found. There are other answers here that go into depth about the WHYs. Fertilizer should always be balanced, compost and fish fertilizer do not meet the qualifications. Fish fertilizer is good but really only those that understand fertilizers should ADD anything to their POTTING SOIL other than an extended release balanced fertilizer. If you add a balanced NPK plus micro nutrients that fish fertilizer which adds nitrogen might make the nitrogen higher in percentage to the phosphorous and potassium and THAT might cause your plants harm. Lettuce needs higher nitrogen because you want the leafy stuff. Too high of nitrogen and plants will not flower and fruit well.
Fertilizer, fish emulsion, blood meal and all the other additives are NOT food for your plants. They primarily give soils the chemistry plants HAVE to have to do photosynthesis and make their own food. Fertilizer does nothing to 'revive' soil. Dump this old soil in your garden. Only decomposed organic matter improves soil's tilth and feeds the soil organisms. That is the only way to improve GARDEN SOIL. Potting soil is different and you are correct, baby plants should not have fertilizer until they are a bit more mature.
Potting soil is sterilized and made for pots. Actually very little soil is in potting soil. And don't get potting soil with fertilizer or any moisture holding gimmicks like sponges or gels. Potting soil is cheap and gives you a chance for success. I know an awful lot about plants, soils, fertilizer and I would NEVER make my own potting soil although I DO know how.
What was planted in your old soil? What insect eggs or pathogens are harbored in that soil? Sure plants will grow but not as vigorously as they would in a pot in potting soil. Success will be iffy. Lettuce is fun to grow.
Please start by germinating seeds in tiny pots...made to start seeds. Using fresh out of the bag potting soil. Germinating or planting too tiny starts into a large pot with a large body of soil, will not be very healthy and is basically a no no. Start seeds in those little peat pots and when the roots show through the bottom UP POT to a size larger....3-4" pots. Use fresh potting soil and now is a great time to add an extended release fertilizer. OSMOCOTE, 14-14-14 is what I recommend even though it is by Scott's. You will need to add a little more when up potted to their larger pot but after than you are done with adding fertilizer.
When the roots show through the bottom in these larger pots, then I would try planting into a larger pot. I usually end up transplanting 3 - 4" starts into a 1 gallon pot (6") for all single vegetables and leave my large pots for tomatoes, or potatoes or squash. `1 gallon pots grow a great head of lettuce, peppers, basil... Do not water deeply until the plant has enough roots integrated into the body of soil (helps to remove water, allowing more air). Then you should start watering deeply and allow the soil to dry (inch below surface dry) before watering again. The larger the plants get and taking into consideration warmer weather the more they will need water but NOT everyday.