My son, in my opinion has a lot of toys. However, not as many as most of his friends. We usually only buy for birthdays and it is only a few presents, one from us and he will have a very small party. All together he has:
lots of books
xbox and three batman lego games
Thomas the train building blocks
That is about it and some stuffed animals. All he plays with is the xbox and the spiderman and batman figurine,, he may hold when watching tv or eating. He loves lego but will only play if we build with him, which I do and that is it.
Should he have more toys? Is he too old for little people's sets?
He also got a bike for his birthday from us.
Should he have more? That's totally up to you and your family circumstances. I do find that I think my kids have "too much" , but they are very resistant to paring down the collection. So we box up and rotate things in and out of the garage, so things stay "new".
If you're looking for ideas for something different, consider building toys. Classic blocks, or magnatiles. I can't remember if it was at 4 or 5 that my boys got magnatiles for their birthday. Those have been wonderful and still get play.How they play with them changes. Right now, the whole set is contructed to be a giant battleship that they've stuffed most of their playmobil knights in to.
There's a lot of neat toys available in catalogs like Magic Cabin or Hearthsong.
Kids can grow without any toys at all- their hands, dirt, sticks, and rocks are enough! But I am surprised how short your list is. I think most kids age 4 need a chance to play with more things than you listed.
I'd consider adding some of these items:
musical instruments- shakers, xylophone, bells, tambourine, keyboard, whistle, flute, harmonica.
active toys- several balls, hula hoop, shovel/bucket, roller skates, skateboard, scooter, helmet, frisbee, bubble blowing set, chalk, tent, watergun, pool noodle, watering can
dramatic play- play food, toy dishes, play vacuum, cash register, doctor set, costumes, hats, masks, puppets
art toys- crayons, markers, color wonder sets, easel, paper, scissors, glitter, glue, glue sticks, magazines to cut, colored pencils, modeling material like playdough, clay or floam, cookie cutters, stencils, bingo markers, stickers
bath toys- foam letters, pour/fill containers, tub markers, duckies, a doll or animal to wash
games- hi-ho-cherry-o, candyland, trouble, elefun, hungry hippos, old maid, memory
And he is definitely not too old for his Little People sets. Most children enjoy figure play (making stories for the little people to do) throughout the K-3rd grade ages.