Is 85 too old to move?

Elowen33.
Illegal Drugs have been delivered by post and/or courier for years, so I don’t know where you got that from. I do know this to be a fact as I had to deal with them when I was working and I took early retirement in 2000 after many years’ service.
This can never be stopped and the Police, Border Force and the National Crime Agency can only do so much.
All the while there is a demand, there will be suppliers.

Before you do the drastic thing and leave - do try the obvious solutions first -

The Housing Association, (with a letter signed by a group of seriously worried tenants, hinting that a mass exodus is on the cards)
Citizens Advice
AgeUK
Police
Your MP, even if you don't like his politics
Local newspaper

Moving out seems extreme as I think there can be financial consequences in finishing these leases.
What are the other resident's views?

Whatever you do don’t give up your tenancy!

Btw, you can FaceTime the dealer in China.

Elowen33
Drugs have been delivered by post for years, and it’s even more prevalent now than it was 10 years ago when this article was published.

www.bbc.co.uk/news/uk-scotland-34400778

If there are noise and anti social behaviours it is likely that the tenant will be evicted at some point, so I would stay put for now. neighbours in a new area could be worse.

Drugs are not delivered by post so i dont see that as relevant, if you know how many packages they receive maybe you are spending too much time watching this person which is only upsetting you more.

I wouldn’t move, they will probably move before you. Can you get on your council/ local MP. Drugs is everywhere unfortunately- especially now certain people want laws around cannabis relaxed.

I wouldn't think your age should be a barrier as you could get help with the removals but are you sure it wouldn't be preferable to address this antisocial neighbour problem first?

You are speculating that things will get worse but you don't know for sure.
You like where you are. There's no guarantee another flat would be better. A private landlord v a housing association? I would think the HA safer.
Could you begin by telling the HA about the antisocial one.
Then ask citizens advice.
There are always options.