The only problem with this is that you paid more than you needed to.

An Adult pass would be valid for a 26 year old so you can still use it.

Other option is to refund it and buy a youth pass. As long as it wasn’t a special offer or you haven’t already used it you should qualify for a refund. Check the conditions here:

https://www.eurail.com/en/eurail-passes/ordering-info/refund-exchange-policy

You should calculate the difference in the amount of refund you will get (85% of purchase price) with the cost of a Youth pass.

If you do decide to refund there is no need to wait for that to be processed before buying the replacement.

Junior pass is about 25% reduced-so all in all with 15% fee you ´gain´ 10% of full price. Plus that due to giant staff shortages you likely will have to wait a few monthes till the money comes back in your bank. Decide yourself what it is worth to you

Hi AI_G and mcadv, thank you very much for the advice. Actually, I had bought it with 'plus', so it would be refundable at 100% instead of 85%, which means the difference would be (25% of price - cost of plus). But you're right about the time I may need to wait for the refund, I'll do some calculations first. Thank you again ^_^

You do not want to request a refund but you want to do an exchange, which should only cost 15€, see the link posted.