Vauxhall Vectra start

i have got a 2003 vauxhall vectra,when i start it in the morning ,it can be slugish or slow to start and then i get a puff of white smoke out of it .. then bit slugish, to get going then it fine .(i have looked at the web and came up with 2 answers, i am told that the valve stem seals are worn, or it just cold , and it condisation.. so i am no better off.., so could do with the help/advice
i have allready spoke to the car dealer whom i bought the car off and he says it due to the age and being near 10 year old, but think he talking crap..
must say it just puffs out smoke in the morning or been sitting, for a while, other times it grand no smoke, and not slugish.. another thing notice was when i drive about 40 mins or so the temperature, rises on the gauge to 80 celsius(which is the 3rd marking on the gauge), the gauge itself only goes to 100 celsius before there is 3 red marks at the end