DS 3.5 was at the slower end of normal to speak (first words around 18 months) but has always understood everything we have said to him, complicated commands etc. As far as I can assess from looking online, he has hit all the speech and language milestones (3 word sentences before 3 etc). Now at 3.5 (july birthday) he is capabale of talking in pretty long sentences and is starting to tell me when things hurt, when he bumped his head etc and asks lots of where, what's that, who is that questions. Nursery seem to have no issues about his speech. But I have noticed that he is very patchy- when he is tired or feels under pressure he either doesnt want to speak or his speech can be very garbled. Still mixes up he/she and you/I occasionally. and the rest of his speech can be grammatically perfect or atrocious. and absolutely no why questions or understanding of the concept why. Good at colurs/numbers/letters/describing things which happen in books etc. More patchy on telling me what he has done that day. In fact says very little about nursery other than that he played with aeroplanes...
He has always been a lateish althpugh within the normal range developer with everything.