You are doing great - keep reading and talking to him. One day he may be interested, the other day he may not. If he has too many toys out at the same time, he may be overwhelmed and not sure what to play with. So maybe put most away and rotate what you keep out so he thinks he is getting something new all the time which will peak his interest.
I work full time.. and when I am at home I try to make the most of my time with my 23 month old as well. I read to him, play puzzles, etc. The key is to constantly talk to him... and know when is enough. You don't want to force it on him, otherwise he will not learn to love to learn. He will eventually listen and become interested on his own time! Just continue to give him opportunities to learn.... He can even learn colors, etc. just by watching you make dinner if you point them out to him!!!
My little boy is 23 months and he already knows the following perfectly. 1) knows his entire alphabet, can say and recognize 2) knows numbers 0-10. 3) knows 8 shapes 4) knows 4 colors 5) knows all body parts, including ebows, knees, toes, fingers, etc.
All I do is read and talk to him and point things out to him.
But don't feel bad if he is not so eager to learn.... my child is unusually quick to pick things up (or so I am told from daycare)
Hang in there.... they all learn things on their own pace. Ignore the milestone books and continue to read and talk to him. That is the quickest and most fun way for them to learn!! And most importantly - Enjoy every minute.