My relative is 60 years old, he has 10 years of cycling experience when he was young, now he has serious arthritis, but still want to ride to the parade,
at the same time I don't know whether electric bike will aggravate his condition?
How to choose a suitable electric bicycle for the elderly?

Test ride some if they're available in your area, read about "best bikes for seniors" (try YouTube) or procure a Lectric Cycles light ebike for circa $800.

First, 60 isn't "elderly". Second, does he have good mobility and good balance? If not, you may want to consider a step-through, something with a low step-over height, or a tadpole recumbent. All of these can be found electrified.

Oh, I really shouldn't have called 60 "elderly" .Thank you for reminding me. But I think he might not like tadpole recumbent, he doesn't really want to travel lying down, he has a certain balance, so a light electric car would be more suitable for him?

Ok, that sounds good. Thanks for the advice.

I ride an electrified tadpole recumbent. Some have more upright seating so they are easier to get in/out of and have better visibility (check out the Catrike Villager for example). I love it, I ride 2-3x the distance I used to ride on my upright 2 wheeler because there is absolutely no discomfort even after 4+ hours. Also, drivers tend to give me a lot more room and respect on the trike than they ever did when riding my 2 wheeler. Talk to your relative......at 60 he may/may not have some physical issues to consider and is capable of deciding what is of interest.
Kudos to you for being concerned.

As you said, when you are 60 years old, you may not care about your physical condition, more should be spiritual enjoyment, I think I should ask my relative's opinion, rather than me to help him decide. Thank you for sharing your story with me, and wish you health and happiness all the time.

Here's an example of a recumbent trike where the rider isn't anywhere near "lying down." (Catrike Villager). It's also available electrified as the Villager eCat.


https://www.catrike.com/villager-ecat $5350, which is considerably less than some e-bikes.

And you bet you shouldn't be saying someone 60 yrs old is "elderly."