tay yetişirse at dinlenir oğul erleşirse baba dinlenir

I assume you left an important letter from your quote.

I guess this may also be a proverb saying -

If a young horse (colt/filly) is fast enough to catch up, the (older) horse will relax, if a son settles down, the father will relax.

thank you very much

Actually henry there is no mistake. "erleşmek" is a verb and it means "to be a man"

Thanks Gokuyum. I couldn´t find this verb in any of my dictionaries, or this site´s dictionary, or the usually reliable tureng.com website.

Is this an old word that is no longer in use?

This is a local verb. er-leş-mek

er (noun) means man, soldier

leş is a reciprocal verb suffix but here it expresses a transformation.

yetişmek has a "to grow" meaning other than "to catch up"

For example in Turkish yetişkin means grown, adult.

If young horse grows, horse will rest; if son grows, father will rest.

 As opposed to the phrase old people often grumble when they have to get up and do a job themselves: "wear the old ones out first"!

Bu in wich language?