Please have stern words with me about assertiveness!

[Idontmeanto]

I’m very aware of a younger, male colleague trying to manage me. He’s more experienced in this field, but less well qualified than myself.
Silly stunts like shutting a door on me when a colleague asked for a discrete word (with both of us about supporting a junior colleague,) and trying to give direction where it’s not required.

He also pulls a lot of trying to socially ingratiate himself with management.

I know I need to be a bit more assertive about this stuff, but I’m a bit asc and middle aged career changer and need a prod.
Help

Challenge it loudly everytime. Why did you shut the door in my face? Thanks for your input in future I will ask if I need your opinion.

Another good stock phrase is what did you say? Pretend not to understand and follow up with why would you need to tell me that?

Are you saying this colleague shut the door with you on the outside? If so, I would have addressed it at the time, by just opening the door, walking in and sitting down as if nothing had happened. Don't bat an eyelid or register that anything happened just focus 100% on the colleague asking for advice. If you've heard of the term Grey Rock, that's how you have to be with him, blank, no reaction.

How does he try to manage you? If he orders you to do something, you could try just not responding but not doing it. If he later asks if you've done such-and-such, just say matter of fact " No I haven't" no apology or explanation. You've got your own work to do, right?

Yes! I do mean he literally closed the door on me. I very stupidly panicked, did nothing and caught up with other colleague later, who was clear she did want me included.

Stupid stupid, this is why I need a kick!

He tries reminding me what I need to be doing, I’m better at dealing with that. I can show up to meetings organised etc. and just let him look daft.

He has a lot of “professional presence” and has decided I can be brushed over although I have a lot of expertise. There are three of us at our level. The third is a younger bloke. In a blokey banter way he tries to undermine him too.
I suspect management are glad we’re a bit competitive.

Oh, and of the three of us, I’d be the hardest to replace. Intellectually I know this.

Hmmmm what a completely unprofessional thing to do - you know how to handle it in future if he tries to do the door thing again. I’d also want to challenge him after the meeting.

You can respond to his reminders with questions such as “I’m aware of what I need to do in my job, why do you feel the need to remind me?” and “Thank you for your concern but your help is not needed or wanted” or even “Why are you so concerned with my tasks, are struggling with your work load and need my help?” (These are all slightly passive aggressive though) I often challenge behaviour like this and my approach usually works but I do recognise it doesn’t work with everyone.

You being prepared and quietly confident can often be seen, he can bluster around but good managers will see exactly who is more competent. Still worth stopping him undermining you though

I'd start making notes based on his behaviour (including the door closing incident). When you have a good list of things book a meeting with him and go through the events that give you 'professional concern' and say you're highlighting this as a concerning pattern of behaviour in case he doesn't realise the effect his behaviour has on you. Request from this time forward that he desists. At this stage don't give any ultimatum, give him fair chance to mend his ways. Be prepared for him to deny, say it's your imagination and aren't you sensitive etc. Don't argue, just note his comments.

If he fails to respond or ramps up the action, then turn it into a formal grievance, including the fact that in the informal meeting he denied it and failed to respond to your request.

btw he sees you as a threat.

No, he sees me as a pushover! He’s asked to take an interest in a project of mine, because it’s very cool and high profile.
He can fuck right off with that one!