Word for a person who learned something in the past, but is now back down to beginner level?

Solution 1:

The OP has asked me to post my comment as an answer.

If the future employee had several years of experience in the trade, he is still experienced; if several years have passed since he was last employed, then I'd say “formerly skilled”, “previously trained”, “semi-skilled”, or “in need of retraining”.

If you remain an [software] engineer until retirement then you need to be prepared to constantly learn new tools and techniques in order to remain relevant. Generally speaking, you will need to be able to fully retrain yourself roughly every 4 to 6 years (while still working full-time). The only way to do that without burning out is to love what you do.

Source: Quora

Solution 2:

In England we would simply say he was out of practice.

This meets your requirements perfectly: it expresses that the person is not currently proficient, but that they used to be, and that their current lack of aptitude is simply a result of having not practised, rather than through any shortcomings that they might have. It is therefore very polite.

out of practice: not currently proficient in a particular activity or skill through not having exercised or performed it for some time.

"he was out of practice at interrogation"

synonyms: rusty, unpractised

_{Source: Oxford Dictionaries (accessed March 16, 2016)}

Solution 3:

This person can be called an erstwhile expert, which suggests that the person used to be proficient, but is currently not anymore.

erstwhile - former; of times past (dictionary.com)

Solution 4:

One word often used is lapsed.

This is particularly used for professions where certification is required to practice and a regular test or experience is required to retain the certificate. A lapsed indivdual has the experience but must resit the examination to practice.

The word is also used in a religious context for people who no longer follow a particular church.