I think a lot of babies go through a phase around 3-4 months where they genuinely seem interested in solids and really want to eat, but I found (with my daughter at least) that it was just an extension of the fact that she wanted to explore EVERYTHING within reach at that age.
Honestly, it's probably not a great idea to feed a 3.5 month old solids, in my honest opinion.... Generally, signs of solid-readiness include the baby being able to sit on his/her own, use a pincer grasp to hold food (that's thumb and forefinger), etc. Six months seems like its really the minimum. I know my daughter didn't really get interested in solids as a nutrition source until she was about 18 months old. We started introducing her to them around 8 months or so, but she really wasn't that into it besides as another toy.