Can a single person give a good advice ?

It's up to the person and advice u lookin for....

Too vague sweetie

We need more info on what you're looking for in an answer

Not if you are asking about something personal and you are asking strangers.

They can offer an opinion.

And then you get to decide whether or not it's "good."

anyone can give advice on anything based on either personal experience or observing life's patterns.

for example, I'm not a mom but raised a nephew to the age of 9 and worked with kids and families for almost 20 years. so I often give parenting advice based on what I've seen over the years.
so yes, anyone can give advice.

I think any person can give good advice if they fit into this criteria.

Experience or knowledge.
If said person can separate from themselves and put themselves into the situation without personal gain in any way.

I also think there are the exceptions to the rule.
For example.. my 16 year old granddaughter is what I would call an old soul and her advice sometimes amazes me at how insightful it is.

And there are many times that I take it and she sure hasn't lived as long as I have.

Only if that advice is from me