Whiney 5 Year Old

He's being whiney/bossy now, due to age, and also because there is a lot of change in his life right now.
It is transitional.
Not a permanent trait.
In an adult... this would be expressed probably as being grumpy/irritable/stressed. But in a child... their "coping" skills are different... they get whiney/grumpy and may, act out.

Talk to him... about it. Let him express himself, even about apprehensions. Let him know, its cool/fine, but you know its hard to know things when you aren't there yet. Adults are like that too.
And, he will make new friends etc. and it will be FUN.

Perhaps, go by his new school, let him S. it etc., before he actually starts.

Don't scold him, for having uneasy feelings.
If my Husband yelled at me or criticized me for things I was apprehensive or nervous about... I would then NOT tell him anything nor trust him to help me.
Same for a kid. They need, understanding or just to say it and know their Mom/Dad Understands....

Kids this age, do not have 100% coping skills. Not even some adults have coping skills.
So for a 5 year old, realize he is a child.
Help him.... express what he is feeling.
Boys... REALLY need to be allowed to express their feelings, and to learn that its okay to do so.

TEACH your son, HOW to express his feelings... and the NAMES for feelings. I taught my kids that from when they are 2 years old. They are now very adept at KNOWING themselves and their feelings. A kid does not know this.... automatically. It needs to be taught to them.

My son who just recently made 6, the other night... I had disciplined him because he was being naughty. So I scolded him. He simmered down... but then he told me "My heart is sad Mommy... my heart really hurts...." And I asked him why. He said... because, I was unhappy with him and it makes him sad inside... and then he apologized. He told me... "My heart never was this sad before..... " and he was crying a bit. I allow.... my son to always express himself to me... bad or good, grumpy or happy. And it helps a child... to cope and to learn how to "manage" feelings. If their parent... discerns the scenarios.

Did my son move into your house???!!!
My son also is going to kindergarten this year. For 3 years he's talked about how cool it would be when he went to kindergarten........now the times finally near and he's excited but anxious. If I mention kindergarten at all he starts to get irritable.
Best of luck - I hope (and I am sure he will) get back to being himself soon.

Not sure what your question is, but my five-year-old sort of does the same thing. She gets pretty overwhelmed, and it was at its worst when she was in daycare. There's so much going on in daycare, like sensory overload, and nowhere to hide from it to be alone. I always make sure to give my girl the time she needs to decompress from the day- in her room by herself, quiet, no demands- or else she is impossible to deal with.

Once he gets used ot his new routine, he'll calm down. Not sure I'd punish right now, as long as his behavior isn't too bad.

He has had a lot of changes. I would try more love and attention instead of time outs and taking away privileges. I thing he is just feeling insecure.

If it's only been this summer, it might be the anticipation of the changes coming. He might be feeling some anxiety and acting out. My daughter starts kindergarten next week too - she just turned 5 and she knows where she is going is a totally different place from where she's been at preschool and child care the past 3 years, with all new kids and teachers. She says she is excited, and not nervous, but sometimes she seems caught in-between wanting to be a more independent "big kid" and wanting to still be a "little kid" and have everything stay the same.

I would still discipline him for poor behavior but make sure you take the time to spend some quality time with him, cuddle on the couch, let him know how proud you are for all the growing up he is doing. Maybe visiting the school and meeting the teacher a few times will help? Hopefully once he adjusts to the changes after starting, the more he will settle down.