10 SEER air handler in small compartment

[Bienes Raices]

The house my offer was accepted on has a 10 SEER air handler that's 17 years old (original with house). It's inside a small wall compartment in the house. The outside heat pump is only four years old though.

Although the air handler performed ok during the inspection, the inspector said it might have to be replaced soon because of its age.

I've heard that all new ACs have to be 13 SEER at least. I'm wondering if a new 13 SEER air handler a) wouldn't fit in the wall compartment because of the size of the larger coils. In that case, what are options do you have? b) I would end up having to get the heat pump outside replaced too because it won't be compatible with the new 13 seer air handler?

I don't know if I should walk away because of this. Thanks.