Hi A.!!
I did put my son in preschool at age 3 but only part-time (Tues. & Thurs. 9a-noon). He went for one year on that schedule and he loved it. I would have put him in 5 days (9a-noon) his 4 year old year but we got transferred to Miami and I was unable to find something I was comfortable with. Now 9 months later, I am trying to find something for my 2 year old daughter part time and it is next to impossible where we live to find part time and if I do it is not some place I would be willing to put her. But I would say if you find a place you feel good about you probably want to start part time. That is for you and him both!!
Hope I have helped some. If you find some place you really like will you let me know. Otherwise my daughter will spend another year at home with me being socialized through playgroups, I suppose.
Good luck,
D.