I do not think there’s any reason to conclude that you cannot achieve stream entry in this lifetime. But, I suspect the way you’re approaching this might not be very helpful in your spiritual practice.
If someone has the capacity and willingness to practice (barring conditions like those mentioned in AN 6.87, and even there the I interpret the ‘dull, witless, etc’ to imply severe mental disabilities), how is it possible to know who and who cannot achieve stream entry in this lifetime? If someone practices for 50 years and does not realize stream entry, does that mean they cannot achieve it in this life, or does it mean they just need to keep practicing? This kind of questioning does not seem to be useful. (By ‘practice’ I do not mean just meditation.)
Also don’t forget to look at what the suttas say about the Saddhānusāri and the Dhammānusāri.