I put a saddle (no pad) on my colt years ago when he was about 10 months. It was a child's swade western saddle and weighed maybe 5 lbs, if not less. I'd put it on him, leave it there for about 10 seconds and take it off. It started out as off/on/off/on to get him used to the saddle being thrown around him. When he didn't seem to care, I started "tightening" the girth, never making it even close to fully tight, just enough so he could feel it against his body. And these sessions were never long at all. I didn't want to hurt him. It really, really helped. For the rest of the time I owned him, he couldn't give a care about a saddle. The older he got the tighter I'd make the girth. When he was about a year old I put a regular saddle on him and acted like I was going to ride. (I waited until he was 2.5 to actually sit on him). I don't know if it was wise of me to do that at his age, and I'm sure others would disagree to start them that young, but I knew my colt from the moment he was born and we had a really strong bond. I think it really helped. Just don't overdo it or push him to far.
Hope that helped. Good luck!
~He knows when you're happy
~He knows when you're comfortable
~And he always knows when you have carrots.