The bigger concern than the need for extensive mixing of paint "more than 25 years old" is that the time puts it closer to when lead (and/or cadmium) was commonly used in virtually all paint products.

A lead-bearing paint should be considered unsuitable for use, especially on anything exposed to children.

Bans on lead in paints in most places probably were well prior to that time (1980s?) but some places continued selling such things for quite a while after they were technically prohibited, espeially in oil based mixes.

If sufficient parts of the label are still visible, you might be able to check for a "contents" list(?) just to be reassured.

John