sugarhoops
No not too late at all, I am just sowing mine now, 
Monty Don did an experiment last year to try and end the on going...."when to sow arguments..but it worked out all pretty much the same", whether you sow early or late, I think the early ones where very slightly ahead, however later may last longer providing no frosts.
Anyway, I usually do them now ish, in seed trays in doors, then plant them out when fear of frosts have gone. This is the balancing act, sew to early and you get them too root bound and you cant put them out due to frost, leave it too late and they take a while to get going but still worth it, as they last till October....
This year I am hardening them off more quickly, and want to sow them out as soon as possible before they become too root bound. I will hold some back in case of frosts, but I want to get them out sooner rather than later.
Cosmos and Zinnia are wonders....both germinate very quickly, so easy to grow and you get soo much value from them, bushy border fillers, on going flowers, wonderful. Again, sow in seed trays or pots and try and get them out before they get root bound, sow now....not to late at all.
Hope that helps.
BTW I grow all sorts of sweet pea but I have noticed the ones that they say could be exhibition have good strong and longer stems, easier to put in vases.