I don't know how to handle DS agressive and boisterous behaviour

[Nanoon]

DS is 3.3 and we also have 10 day old boy.
DS1 is lively to say the least and has been so since well before DS2 was born. He can be loving, gentle and relaxed one minute and can change in an instant into an agressive, boisterous little horror with arms and legs flying everywhere, jumping on people and generally being a nightmare.
I don't know how to deal with his behavour as telling him off seems to make him more aggressive, a warning and then time out just removes him from the situation for 3 minutes and it doesn't seem to deter him and reminding him to be gentle, play nicely etc in advance just seems to give him the green light to bounce around the room.
He is a bright, loving little chap but DH and I spend the whole time braced for the next aboutburst. I am dreading DH going back to work after paternity leave as I have no idea how i'll handle him and a newborn on my own.
Sorry this is so long and if it all seems abit pathetic but i would be very grateful if anyone could give me and tips that worked for them or just to know someone else is in the same boat.
Thanks

It doesn't sound like he's aggressive so much as lively.

I'd try to make sure he gets a lot of 'good' physical play, lots of running about and bouncing in the right places, iyswim. My DS2 is about the same age as yours, and he needs to run and play a lot.

Does he go to playgroup or any drop ins for the social interaction?

And I'm afraid you should be ready for his behaviour to be actually bad for a little bit, since the birth of his brother. A new baby is hard on older siblings.

agree with NQC. I've have two sons, both ultra lively as toddlers and IME it's so important to let them run off what energy they can. It can be frustrating when you look at other 3 year olds and see them being much more calm and docile - for some toddlers, it is jus tnot in their nature, though obviously you have to lay down rules like time outs(as you are doing.